cmd: Add MR show command

[nkprince007]

No description provided.

[codecov]

Codecov Report

Merging #69 into master will increase coverage by 0.71%.
The diff coverage is 65.62%.

@@            Coverage Diff             @@
##           master      #69      +/-   ##
==========================================
+ Coverage   56.64%   57.36%   +0.71%     
==========================================
  Files          22       23       +1     
  Lines        1038     1100      +62     
==========================================
+ Hits          588      631      +43     
- Misses        299      308       +9     
- Partials      151      161      +10

Impacted Files	Coverage Δ
cmd/mr.go	45.45% <25%> (+5.45%)	⬆️
internal/gitlab/gitlab.go	32.57% <50%> (+0.65%)	⬆️
cmd/mrShow.go	75% <75%> (ø)

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[zaquestion]

Looks good, 1 requested change and I'm gonna merge this in as is since need to make the same change for issue too.

[zaquestion]

It seems like the Long and Short descriptions should stay how they are since the mr cmd has other functions under it. I realize I let this slip on the issue command, am intending to fix that before release. Potentially we could not in the long description that lab mr 1 will do a show