feat: allow specify the context to be added

[cr7258]

Description

Implement: #952 (comment)
Add a new parameter --context to specify the context to be added when running kubecm add or merge command.

Test

Prepare two kubeconfig.

./kubecm list --config kubeconfig1
+------------+-------------+-------------+----------+-------------------------+--------------+
|   CURRENT  |     NAME    |   CLUSTER   |   USER   |          SERVER         |   Namespace  |
+============+=============+=============+==========+=========================+==============+
|      *     |   context1  |   cluster1  |   user1  |   https://example1.com  |    default   |
+------------+-------------+-------------+----------+-------------------------+--------------+

./kubecm list --config kubeconfig2
+------------+-------------+-------------+----------+-------------------------+----------------+
|   CURRENT  |     NAME    |   CLUSTER   |   USER   |          SERVER         |    Namespace   |
+============+=============+=============+==========+=========================+================+
|      *     |   context2  |   cluster2  |   user2  |   https://example2.com  |   kube-system  |
+------------+-------------+-------------+----------+-------------------------+----------------+
|            |   context3  |   cluster3  |   user3  |   https://example3.com  |     default    |
+------------+-------------+-------------+----------+-------------------------+----------------+
|            |   context4  |   cluster4  |   user4  |   https://example4.com  |     default    |
+------------+-------------+-------------+----------+-------------------------+----------------+

Specify context2 and context3 to be added.

./kubecm add --config kubeconfig1 -f kubeconfig2 --context context2,context3

# result
+------------+-------------+-------------+----------+-------------------------+----------------+
|   CURRENT  |     NAME    |   CLUSTER   |   USER   |          SERVER         |    Namespace   |
+============+=============+=============+==========+=========================+================+
|      *     |   context1  |   cluster1  |   user1  |   https://example1.com  |     default    |
+------------+-------------+-------------+----------+-------------------------+----------------+
|            |   context2  |   cluster2  |   user2  |   https://example2.com  |   kube-system  |
+------------+-------------+-------------+----------+-------------------------+----------------+
|            |   context3  |   cluster3  |   user3  |   https://example3.com  |     default    |
+------------+-------------+-------------+----------+-------------------------+----------------+

Specify context1 and context2 to be merged.

./kubecm merge kubeconfig1 kubeconfig2 --context context1,context2

# result
+------------+-------------+-------------+----------+-------------------------+----------------+
|   CURRENT  |     NAME    |   CLUSTER   |   USER   |          SERVER         |    Namespace   |
+============+=============+=============+==========+=========================+================+
|            |   context1  |   cluster1  |   user1  |   https://example1.com  |     default    |
+------------+-------------+-------------+----------+-------------------------+----------------+
|            |   context2  |   cluster2  |   user2  |   https://example2.com  |   kube-system  |
+------------+-------------+-------------+----------+-------------------------+----------------+

Specify the contexts to be added after overwriting the name with the context template.

./kubecm add --config kubeconfig1 -f kubeconfig2 --context cluster2-user2,cluster3-user3 --context-template cluster,user

# result
+------------+-------------------+-------------+----------+-------------------------+----------------+
|   CURRENT  |        NAME       |   CLUSTER   |   USER   |          SERVER         |    Namespace   |
+============+===================+=============+==========+=========================+================+
|            |   cluster2-user2  |   cluster2  |   user2  |   https://example2.com  |   kube-system  |
+------------+-------------------+-------------+----------+-------------------------+----------------+
|            |   cluster3-user3  |   cluster3  |   user3  |   https://example3.com  |     default    |
+------------+-------------------+-------------+----------+-------------------------+----------------+
|      *     |      context1     |   cluster1  |   user1  |   https://example1.com  |     default    |
+------------+-------------------+-------------+----------+-------------------------+----------------+

Related Issue

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [] Documentation update (changes only affecting documentation)

Checklist

• I have tested my changes locally and ensured they are functioning properly. Please run the make build and make test commands.
• I have added/updated unit or e2e tests to cover my changes.
• I have updated the relevant documentation. If you change commands or arguments, run make doc-gen to generate new documentation.

[the-label-bot]

The Label Bot has predicted the following:

Category	Value	Confidence	Applied Label
Kind	feature	0.800	✔️
Kind	L	0.855	✔️

[codecov]

Codecov Report

Attention: Patch coverage is 18.75000% with 26 lines in your changes are missing coverage. Please review.

Project coverage is 19.68%. Comparing base (67886bf) to head (b38e4f3).
Report is 1 commits behind head on master.

Files	Patch %	Lines
cmd/add.go	37.50%	9 Missing and 1 partial ⚠️
cmd/cloud_add.go	0.00%	10 Missing ⚠️
cmd/merge.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #962      +/-   ##
==========================================
+ Coverage   19.65%   19.68%   +0.03%     
==========================================
  Files          21       21              
  Lines        2122     2134      +12     
==========================================
+ Hits          417      420       +3     
- Misses       1661     1670       +9     
  Partials       44       44              

Flag	Coverage Δ
unittests	19.68% <18.75%> (+0.03%)	⬆️

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[sunny0826]

LGTM
Thank you for your valuable contribution to this project! Your work is greatly appreciated. 🎆