Need to switch all Travis PR builds to an alternative ASAP

[aaime]

Travis is de-facto shutting down free services for open source projects (gives a modest amount of build credits, will last us a few days). We need to move those builds to another provider, like:

• GitHub actions
• CircleCI
• Azure pipelines

Builds are now pretty slow, but they will be shut completely in a matter of a few days at most (there is no deadline, they are migrating projects to the paid for offering bit by bit, plan to be done beginning of december).

@simboss the community already knows but there is no activity in this regard, I guess it's up to us.

Travis builds now cover the most significant bits, including:

• Linux JDK 8 and 11 builds
• QA
• In GeoServer, documentation and packaging checks
• In GeoTools, tests on databases such as Oracle, SQLServer and MySQL

[simboss]

@aaime schedule a call to discuss options and costs

[aaime]

Brad Hards noticed yesterday's PSC meeting logs and started migrating jobs to GitHub actions. Not sure how far he will get, seems he won't migrate all builds (the database ones in particular might not be migrated, but the situation is evolving, PRs are out and being updated as I write)

[aaime]

Brad and Mark have been doing all the work (including all of the databases), assinging to myself just for the sake of review and merge