Add API to get domain

[zychen5186]

Why are the changes needed?

1. While integrating interactive CLI into flytectl, I would need to allow users to select the domain for the project in commands like flytectl get execution.

What changes were proposed in this pull request?

1. Add GetDomains API in flyteidl
2. Server GetDomains implementation in flyteadmin,
3. Client GetDomains implementation in flytectl

How was this patch tested?

Tested by running flyteadmin with dev cluster and called the GetDomains function in AdminFetcherExtClient by flytectl.

Added unit test to:

1. flyte/flyteadmin/tests/project_test.go
2. flyte/flytectl/pkg/ext/domain_fetcher_test.go

Setup process

flytectl demo start --dev
POD_NAMESPACE=flyte ./flyte start --config flyte-single-binary-local.yaml

Screenshots

Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

Related PRs

In order to support domain selection in interactive CLI

Docs link

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 12 lines in your changes missing coverage. Please review.

Project coverage is 61.34%. Comparing base (297cdf8) to head (13551b4).
Report is 133 commits behind head on master.

Files with missing lines	Patch %	Lines
flyteadmin/pkg/rpc/adminservice/project.go	0.00%	10 Missing ⚠️
flytectl/pkg/ext/domain_fetcher.go	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5443      +/-   ##
==========================================
+ Coverage   61.01%   61.34%   +0.32%     
==========================================
  Files         793      791       -2     
  Lines       51419    51040     -379     
==========================================
- Hits        31372    31309      -63     
+ Misses      17155    16851     -304     
+ Partials     2892     2880      -12     

Flag	Coverage Δ
unittests-datacatalog	69.31% <ø> (ø)
unittests-flyteadmin	58.72% <60.00%> (-0.03%)	⬇️
unittests-flytecopilot	?
unittests-flytectl	68.03% <60.00%> (-0.01%)	⬇️
unittests-flyteidl	79.04% <ø> (ø)
unittests-flyteplugins	61.83% <ø> (ø)
unittests-flytepropeller	57.30% <ø> (ø)
unittests-flytestdlib	65.80% <ø> (ø)

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[pingsutw]

Thank you, some minor comments

[pingsutw]

LGTM, thank you!