feat: Add ability to mark branch to be deleted from update

[zemzale]

Description
This MR adds option to mark branch to be deleted form update command.

Related Issue

#273
Motivation and Context

We can create MR that are marked to be deleted, but we can't update that. This fixes that.
How Has This Been Tested?

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)

Checklist:

• [ x] My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #278 into trunk will decrease coverage by 0.00%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##            trunk     #278      +/-   ##
==========================================
- Coverage   46.15%   46.14%   -0.01%     
==========================================
  Files         113      113              
  Lines        5982     5985       +3     
==========================================
+ Hits         2761     2762       +1     
- Misses       2922     2924       +2     
  Partials      299      299              

Impacted Files	Coverage Δ
commands/mr/update/mr_update.go	27.14% <33.33%> (+0.27%)	⬆️

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[profclems]

Thanks @zemzale! LGTM 🎉