feat(milestone): Add `--start` & `--due` to `create`; Add `browse` subcommand

[claytonrcarter]

This adds a couple things to lab milestone:

• milestone create now accepts flags --start and --due to set the respective dates for the new milestone
  • GL API docs: https://docs.gitlab.com/ee/api/milestones.html#create-new-milestone
  • go-gitlab docs: https://pkg.go.dev/github.com/xanzy/go-gitlab#CreateMilestoneOptions
  • does not add tests for this because there is no test coverage for milestone create anyway
  • I have tested it manually and it worked as expected
  • date parse code was largely copied from CreatePAT in internal/gitlab/gitlab.go
• Adds a new milestone browse subcommand
  • unlike issue/mr/snippet browse, which all accept an id for a specific resource, milestone browse takes the name of a milestone
  • maybe it's just me, but I did this because I never refer to milestones by id, only by name; conversely, I never refer to issues and mrs by title, only by id
  • I did add a simple test for this, because it was really easy 😄

[codecov[bot]]

Codecov Report

Patch coverage: 45.09% and project coverage change: +0.19% :tada:

Comparison is base (644d19a) 55.70% compared to head (653156a) 55.89%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #881 +/- ## ========================================== + Coverage 55.70% 55.89% +0.19% ========================================== Files 82 83 +1 Lines 5953 6002 +49 ========================================== + Hits 3316 3355 +39 - Misses 2349 2353 +4 - Partials 288 294 +6 ``` | [Files Changed](https://app.codecov.io/gh/zaquestion/lab/pull/881?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann) | Coverage Δ | | |---|---|---| | [cmd/milestone\_create.go](https://app.codecov.io/gh/zaquestion/lab/pull/881?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann#diff-Y21kL21pbGVzdG9uZV9jcmVhdGUuZ28=) | `46.66% <29.62%> (-28.34%)` | :arrow_down: | | [cmd/milestone\_browse.go](https://app.codecov.io/gh/zaquestion/lab/pull/881?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann#diff-Y21kL21pbGVzdG9uZV9icm93c2UuZ28=) | `62.50% <62.50%> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/zaquestion/lab/pull/881/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zaq%3F+Wiedmann)

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[prarit]

Hey @claytonrcarter sorry for the late review. I think this looks fine.

[zaquestion]

Thanks for tending to lab folks, it's extremely appreciated :heart: