Add bibliography submodule

[MakisH]

Description of changes:

• add the-teachingRSE-project/bibliography as a submodule of this project
• update the contributing guidelines
• remove the local BibTeX file
  • migrate any contributions from currently open PRs to the new BibTeX repository
  • closes Survey of resources on RSE and RSEing #245

[jngrad]

• Adds a workflow to update the submodules (manually/on a schedule)

I have reservations about automatically updating the submodule revision: any commit in the BibTeX repository would trigger a new commit in N repositories. If the commit contains a syntax error, CI will break in N repositories. At my institute, we introduced CI in the BibTeX repository to mitigate that issue, and required the update to be done manually, so that the individual updating the submodule is also responsible for checking the entire bibliography in the manuscript.

[MakisH]

I can make the workflow manual, that's not a problem.
We definitely don't want a cascade of commits and errors.

[jngrad]

LGTM

[jngrad]

Everything works as expected: the-teachingRSE-project/institutionalized_education#4 and compile action 9319020130.

[MakisH]

From my side, this is ready to merge. I will not join the next two meetings, please go ahead and implement any edits that might pop up.

[CaptainSifff]

I agree, technically this looks great!
I now wonder, what the workflow is for MRs like the changes to 266 by @hvwaldow ...