Add COMPONENT_PR as arguments in components.yaml

[MakisH]

To be able to work with PRs from forks, the COMPONENT_PR (e.g., PRECICE_PR) is being passed by the calling workflow. Since this is not a required argument, it was not declared as one in components.yaml.

#907 changed the build argument parsing from "forward everything the user defines" to "collect whatever each component needs". This ignores the extra arguments. While this is better from a security point of view, it reduces the flexibility that was useful in this case.

As a workaround, this PR sets for each COMPONENT a COMPONENT_PR argument, with an empty string as a default value. Testing without calling from a workflow one does not seem to complain. The TUTORIALS_PR is set in the bare component, as this is the base for everything else.

This should enable working with forks again, which was detected in the context of precice/precice#2601.

[MakisH]

Actually, since now every component uses its own list of arguments (and might be called from arbitrary repositories), I needed to add a *_PR for every *_REF in ae87db6.