feat: Add MergeAsync and GetMergeAsyncResult support

[ymh3090]

Adds support for the asynchronous pull request merge endpoints, needed for merging stacked pull requests (the existing Merge method doesn't support stacks).

• PullRequestsService.MergeAsync — PUT /repos/{owner}/{repo}/pulls/{pull_number}/merge-async
• PullRequestsService.GetMergeAsyncResult — GET /repos/{owner}/{repo}/pulls/{pull_number}/merge-async/{uuid}

Docs:

• https://docs.github.com/en/rest/pulls/pulls?apiVersion=2022-11-28#merge-a-pull-request-asynchronously
• https://docs.github.com/en/rest/pulls/pulls?apiVersion=2022-11-28#get-the-result-of-an-asynchronous-merge

Closes #4485

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[ymh3090]

recheck

[ymh3090]

recheck

[ymh3090]

hi, @gmlewis !
I've signed the Google CLA, but the cla/google check is still failing after a recheck. Could you take a look?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.53%. Comparing base (f9fec07) to head (c2cab06).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4491   +/-   ##
=======================================
  Coverage   98.52%   98.53%           
=======================================
  Files         195      195           
  Lines       17729    17747   +18     
=======================================
+ Hits        17468    17487   +19     
+ Misses        261      260    -1     

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[gmlewis]

Thank you, @ymh3090!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @alexandear - @Not-Dhananjay-Mishra

[alexandear]

Please improve naming for consistency.

[gmlewis]

@ymh3090 - could you please git pull the "merge" I performed on your branch and then change the "Ptr" instances to "new" (due to #4481 ) and push the changes to this PR? Sorry for the inconvenience.

[DP19]

This endpoint can return a 202 AcceptedError - other places where this happens is either handled in the function or documented in the function docs. Not sure what the maintainers prefer but we should do something here

[gmlewis]

It seems like adding a comment in the function docs would be sufficient here - do you agree, @DP19?

[DP19]

ah maybe it should be handled in the function just based on a previous bug #3036 / #3047 - the doc might be fine as long as people don't care about the response in that case. Up to you all!

@gmlewis

[gmlewis]

Since this is an asynchronous call anyway, I think a comment should be just fine. In those other examples, users were waiting for the upload, but here, they are explicitly calling an async endpoint anyway and are planning on waiting. Thoughts?