[1.8.x] Actions for community PRs.

[scottarnette]

Change Description

Problem:

• Travis limits us to a certain amount of jobs at a time for the entire Github org.
• It is also limited on total time a job can run.
• The hardware available is limited and slow.

Solution:

• Replace Travis with Giithub Actions so that we can triple the amount of concurrent jobs.
• Github Actions job timeouts are much longer than Travis.

See:
https://github.com/EOSIO/eos/actions/runs/35947290 | Forked PR. This builds a PR from my fork of EOS to this branch.

NOTE: If all steps in Actions are skipped, the build is marked as failed. The "Start Job" step exists to fix this issue. All build steps are triggered from that step IF the PR is forked.

Consensus Changes

• Consensus Changes

API Changes

• API Changes

Documentation Additions

• Documentation Additions