Create cross-project way to ensure license compliance

[mcomella]

Currently, each team maintains their own license compliance files, which is a lot of duplicated tedious and time-consuming work: we should create a solution to help ensure compliance across teams.

My two ideas, in order of preference, are:

• Automated: generate a licenses file as part of the build step
• Manual: create a pre-push/CI task that ensures a dependencies block cannot be updated without also updating licenses.html (and if there are no relevant changes, we can update a timestamp in a comment in the file).

To share this code, we could use our shared gradle plugin.

┆Issue is synchronized with this Jira Task

[pocmo]

For reference Google has a gradle plugin for that too. But unfortunately it's in Google Play Services and closed-source. But it may still be helpful to look at how this is added to the build and app:
https://developers.google.com/android/guides/opensource

[csadilek]

Moved to bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1795120

Change performed by the Move to Bugzilla add-on.