github-actions: Add bionic frontend and backend test job.
github-actions: Add bionic frontend and backend test job.

Some noteable diffrence from circleci:
   - We upgrade git to newer version (reason explained in comments)
   - We set HOME to /home/github (also explained in comments)
   - Adjust permissions (... comments)
   - Minor changes to step names and cache keys.
   - We don't need to port the save_cache steps they are done
     automatically in actions. And, we did not port the
     store_test_results step which is circleci specific.
   - We didn't port the notify_failure step yet (see the TODO).

punchagan/zulip,showell/zulip,eeshangarg/zulip,brainwane/zulip,kou/zulip,rht/zulip,hackerkid/zulip,andersk/zulip,kou/zulip,andersk/zulip,hackerkid/zulip,brainwane/zulip,punchagan/zulip,hackerkid/zulip,rht/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,andersk/zulip,eeshangarg/zulip,eeshangarg/zulip,kou/zulip,brainwane/zulip,eeshangarg/zulip,kou/zulip,brainwane/zulip,eeshangarg/zulip,hackerkid/zulip,rht/zulip,showell/zulip,brainwane/zulip,brainwane/zulip,showell/zulip,eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,andersk/zulip,punchagan/zulip,showell/zulip,showell/zulip,rht/zulip,brainwane/zulip,zulip/zulip,punchagan/zulip,rht/zulip,hackerkid/zulip,kou/zulip,eeshangarg/zulip,showell/zulip,kou/zulip,andersk/zulip,rht/zulip,zulip/zulip,showell/zulip,andersk/zulip,zulip/zulip,zulip/zulip,andersk/zulip,zulip/zulip,hackerkid/zulip,kou/zulip,rht/zulip,punchagan/zulip