Bug 2021009 - Add mach try for enterprise

[lissyx]

The matching changes on taskcluster are https://github.com/mozilla/enterprise-firefox/pull/581/files/b5c566488fc0911766e905f07fa7710f7f0cd9ba#diff-8d55b0b4fa50a5d12dc201130b1868dace2ed758cfe9fd3458be0ed3438d6489:

    "enterprise-firefox-try": {
        "enable_always_target": True,
        "release_product": "firefox-enterprise",
        "target_tasks_method": "try_tasks",
    },

[ahal]

This isn't going to work, I looked into it already.

The "pull request" string is tied to the github-pull-request events, and because these are pushes they won't work.

Outside of PRs, Treeherder assumes that a project is tied to a single git branch, so there's no way for it to show "all" branches. This will require a larger refactor and likely database schema changes.

I have some WIP patches to start down this path, but it's not a trivial fix or anything.