feat(mr/view): update mr reviewers

[kousikmitra]

Description
It allowes mr update to update reviewers with a new flag --reviewer. The behaviour of --reviewer is same as --assignee flag but instead it updates reviewers of the merge request.

Note: I have made the flag as --reviewer instead of --reviewers to keep consistency with --assignee

Related Issue

Resolves #562

How Has This Been Tested?
Locally tested with
glab mr update --reviewer +name
glab mr update --reviewer -name
glab mr update --reviewer name
glab mr update --reviewer +name --assignee +name

Screenshots (if appropriate):

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 #694 (2e3738f) into trunk (35e792f) will decrease coverage by 0.30%.
The diff coverage is 35.71%.

@@            Coverage Diff             @@
##            trunk     #694      +/-   ##
==========================================
- Coverage   59.95%   59.65%   -0.31%     
==========================================
  Files          90       90              
  Lines        6450     6496      +46     
==========================================
+ Hits         3867     3875       +8     
- Misses       2218     2250      +32     
- Partials      365      371       +6     

Impacted Files	Coverage Δ
commands/cmdutils/cmdutils.go	70.88% <35.71%> (-2.80%)	⬇️
commands/mr/mrutils/mrutils.go	65.56% <0.00%> (-14.28%)	⬇️
cmd/glab/main.go	40.22% <0.00%> (-0.95%)	⬇️
pkg/iostreams/iostreams.go	39.36% <0.00%> (ø)
commands/mr/view/mr_view.go	76.82% <0.00%> (+1.29%)	⬆️

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[zemzale]

LGTM!

[profclems]

Thanks for working on this @kousikmitra. All looks good now. I added a commit to fix the reviewer action messages

[kousikmitra]

Thanks @profclems :)