Handle approval rules

[prarit]

Add the ability to add, delete, and list merge request approval rules.

Closes #835

Signed-off-by: Prarit Bhargava [email protected]

[codecov[bot]]

Codecov Report

Patch coverage: 8.25% and project coverage change: -0.82 :warning:

Comparison is base (2bbd110) 55.56% compared to head (04dfcfe) 54.74%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #874      +/-   ##
==========================================
- Coverage   55.56%   54.74%   -0.82%     
==========================================
  Files          82       83       +1     
  Lines        5977     6081     +104     
==========================================
+ Hits         3321     3329       +8     
- Misses       2367     2464      +97     
+ Partials      289      288       -1     

Impacted Files	Coverage Δ
internal/gitlab/gitlab.go	8.09% <0.00%> (-0.24%)	:arrow_down:
cmd/mr_approval_rules.go	11.53% <11.53%> (ø)

... and 2 files with indirect coverage changes

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