Integrate fetching latest components into Systemtest.py

[MakisH]

This PR largely simplifies the GitHub Actions workflows by integrating the resolution of the latest commits of each repository directly into the systemtests.py.

The algorithm now is generally:

• Collect all needed parameters (as before)
• Replace any not given needed parameters with their defaults (as before)
• For all parameters ending in _REF, resolve the respective commit from the given repository
  • If this fails, just continue with the ref as-is, and throw a warning.

To achieve that, besides the changes in systemtests.py:

• In the components.yaml, I moved the repository: from the component level to the level of each build argument. This is a bit ugly, but it was the easiest access to the repository. Note that this has to be the same as the remote in the respective Dockerfile (currently not enforced).
• In the components.yaml, I replaced all the default git references to the respective develop branches. The master/main were anyway not really useful. I also removed the description, since these were also not used anywhere.

For the GitHub Actions workflows:

• I removed the nmbgeek/github-action-get-latest-commit action:
  • Simplifies the calling workflows
  • Removes an unmaintained action that is currently throwing Node version related warnings
  • Removes an unreliable dependency, see Latest components workflow hits API usage limits #682
• For similar reasons, I removed the recently introduced VeyronSakai/display-inputs-action, replacing it with a JSON dump of all given inputs.

The workflows can be further simplified and cleaned-up, but that's good enough for now.

I have ran the system tests locally and on GitHub Actions, using branches and tags as given refs, as well as omitting or giving empty arguments. Empty arguments are now assumed to be replaced by the default. Example run: https://github.com/precice/tutorials/actions/runs/27567474586 (the inputs will only be shown once merged to develop, since it reuses the run_testsuite workflow.

Closes #841.

Checklist

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md.