Bug 1949264 - Add git migration compatibility for ./mach try perf

[Andrej1198]

As we are migrating to github away from mercurial we will not be able to see the try revision when we run ./mach try perf. This patch should allow us to be re-directed to the correct compareview links that ./mach try perf will output
Should be used in conjunction with this patch to test locally: https://phabricator.services.mozilla.com/D244392

[Andrej1198]

Hi @beatrice-acasandrei,
As I mentioned I would re-format my PR and have an explanation for what I am doing and why.

Background: Currently we use mercurial locally as a version contral system for developers, as mozilla-central will move away from mercurial and move to github repos we must adjust certain parts of our codebase that will rely exclusively on mercurial, this is one of those things.

The problem: When using ./mach try perf to compare performance we use the --push-to-vcs command to push changes to try and to get a commit id that then used to generate a link that can be viewed easily, the problem is that when we migrate to github we will no longer have access to --push-to-vcs. We need some way to generate a link people can use and share easily and not forget about.

The solution: Treeherder has APIs with an ability to search commit messages for keywords. So when we push the changes to try we will attach a hash consisting of time, author and local commit to generate a unique identifier we can search to find commits and to generate immediate perma-links developers can access when they push to ./mach try perf. The perma link will consist of newHash and baseHash instead of newRev and baseRev. The api we create here will only be used for perfcompare(and potentially for compareview if we decide to keep it after our work wek discussions) to lookup what the revision is for each of the hashes we provide it.