feat(mr create): add --squash-before-merge parameter

[pataar]

Description
This adds the --squash-before-merge parameter to mr create. Which allows the merge request the be squashed by default. See: https://docs.gitlab.com/ee/api/merge_requests.html#create-mr

Related Issue
How Has This Been Tested?
I've used the binary built from this fork against a private Gitlab instance. Worked as expected.

Types of changes

• 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 change)
• Documentation
• Chore (Related to CI or Packaging to platforms)

[codecov]

Codecov Report

Merging #855 (977e830) into trunk (5d497fd) will decrease coverage by 0.04%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##            trunk     #855      +/-   ##
==========================================
- Coverage   59.35%   59.31%   -0.05%     
==========================================
  Files          93       93              
  Lines        7374     7383       +9     
==========================================
+ Hits         4377     4379       +2     
- Misses       2614     2619       +5     
- Partials      383      385       +2     

Impacted Files	Coverage Δ
commands/mr/create/mr_create.go	33.24% <33.33%> (-0.26%)	⬇️
commands/root.go	77.50% <0.00%> (ø)
commands/api/pagination.go	95.31% <0.00%> (ø)
commands/project/clone/repo_clone.go	63.57% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5d497fd...977e830. Read the comment docs.

[pataar]

@profclems Changed it to --squash-on-merge along with #856