Add support for Git Credential Manager (beta-only)

[niik]

Closes #18654
Ref desktop/dugite-native#510
Ref desktop/dugite-native#508

Description

This adds experimental (beta only) support for Git Credential Manager (GCM) which we're now bundling inside of GitHub Desktop's custom Git environment.

When enabling GCM GitHub Desktop will forward all requests for credentials that don't match accounts stored in GitHub Desktop (in essence third party hosts such as Azure Devops, BitBucket, etc).

GCM currently supports Azure DevOps, Azure DevOps Server (formerly Team Foundation Server), Bitbucket, GitHub, GitLab, and generic username + password hosts.

The feature is currently disabled by default and limited to betadevelopment.

Note for reviewers: Hiding whitespace can should help with reviewing changes in git/core.ts.

Screenshots

Release notes

Notes: [New] Option to use Git Credential Manager for repositories hosted outside of GitHub.com

[niik]

Seems we've got some legit test failures here. One of them is related to our use of '--keep-reduntant-commits' in

desktop/app/src/lib/git/cherry-pick.ts

Lines 160 to 173 in afb7d2e

	// --keep-redundant-commits follows pattern of making sure someone cherry
	// picked commit summaries appear in target branch history even tho they may
	// be empty. This flag also results in the ability to cherry pick empty
	// commits (thus, --allow-empty is not required.)
	//
	// -m 1 makes it so a merge commit always takes the first parent's history
	// (the branch you are cherry-picking from) for the commit. It also means
	// there could be multiple empty commits. I.E. If user does a range that
	// includes commits from that merge.
	const result = await git(
	[
	'cherry-pick',
	...commits.map(c => c.sha),
	'--keep-redundant-commits',

Error: GitError: fatal: cherry-pick: --keep-redundant-commits cannot be used with --continue

This was added in git v2.45.1: git/git@bd2f9fd and I have not dug further into it yet. @tidy-dev do you recall the details around this parameter?

The second issue seems to be that our localStorage mock isn't working as intended. Looking into that

[tidy-dev]

--keep-rundandant-commits

Here is some context: #11717

I haven't tested but I believe if you say had commits: A B C D E on a branch and attempted to cherry-pick B C D to another branch where C would be redundant and thus result in an empty commit, it would stop progression and through and error. Apparently the other option was to skip the commits, we went with keep redundant so that commits didn't just disappear. I.E., User cherry-picks 3 but only 2 show up in target branch. A user might be confused about where it went. Possible third option that I didn't explore.. would be capture that error, and putting in the success banner "Redundant commits were skipped"

[tidy-dev]

Looks like --keep-redundant-commits was deprecated.

https://git-scm.com/docs/git-cherry-pick#Documentation/git-cherry-pick.txt---keep-redundant-commits

Maybe we can just swap for --empty=keep - It would appear so from the documentation.

[niik]

Maybe we can just swap for --empty=keep

I think the problem is that we can't use either one in conjunction with --continue. I presume it's enough to keep it in cherryPick but not in continueCherryPick