[PATCHES rtems, source-builder] Add GitHub Actions scripts

[Christian Mauderer]

Hello,

some weeks ago I created a GitHub Actions based CI script that we
(embedded brains) wanted to use to test patches (see
https://github.com/embedded-brains/rtems/tree/ci). I don't think much of
the RTEMS community noted these. I would like to suggest adding the
scripts to the official RTEMS repositories so that the actions are
executed in the official GitHub RTEMS mirrors.

To make sure that GitHub pull requests are not perceived at the official
way to make RTEMS contributions, an auto-responder action notifies the
pull request user that the current way to make contributions is sending
patch sets to devel at rtems.org.

This step will allow users to easily test patches on a number of
simulators before they send them to the mailing list. No one is forced
to do it, but everyone can try it. For RTEMS, it has the advantage that
the patches are at least guaranteed to be compile-clean on a selected
number of BSPs and that they survived a test run on a simulator.

Please note: With this patch I do not intent to push GitHub as the RTEMS
CI or to move from mailing list patches to push-requests. My idea is to
allow everyone to experiment with a proof of concept prototype. Based on
your experiences in this test phase, I would suggest that we have a
review discussion in a month or two to select a suitable way forward for
RTEMS CI. I think after that test phase we all know better what we want
or expect which helps selecting the best CI system that then can replace
this proof of concept system with GitHub.

But now to make make it more clear what we will get with merging these
patches:

You can find a (not yet cleaned up) version of the patches in these
repositories:

https://github.com/embedded-brains/rtems
https://github.com/embedded-brains/rtems-source-builder

The results from a current run on RTEMS are here:

https://github.com/embedded-brains/rtems/actions/runs/3901364934

If you scroll down on that page, you get a summary that shows which
tests fail on three (mostly) randomly selected simulator BSPs. GR740
usually can run all tests but currently jffs2_fsrdwr fails. The full
output of the rtems tester is in the Artifacts in case you want to take
a look at the test output.

If you want to try the CI with some of your patches before we merge this
to the official repositories, feel free to create a pull request to the
ci branches of the embedded-brains/rtems repositories. See the github
manual for guidance how to create a pull request:

  https://docs.github.com/articles/creating-a-pull-request

Note: It is important that you somewhen forked from the official RTEMS
repositories or from one of the forks using (for example) the fork
button in the github web interface. If you just pushed a repo to an
empty one, github doesn't recognize the link and won't allow you to
create a pull-request towards the embedded-brains repository.

Best regards

Christian