PR #588 (issues #520 and #484): Update documentation for get_score_names()

[nikosbosse]

Description

This PR is a follow-up to #588 (related to issues #520 and #484).

I was a bit sloppy in the last PR, in particular with the documentation. This PR

• updates the documentation for get_score_names(), replacing instances of "metric" with"scoring rule" and overall making it a lot more clear what's happening
• adds functionality to warn if column names of a metric have been changed
• adds unit tests
• removes unrelated old tests that are no longer used
• updates the News.md file

Checklist

• My PR is based on a package issue and I have explicitly linked it.
• I have included the target issue or issues in the PR title as follows: issue-number: PR title
• I have tested my changes locally.
• I have added or updated unit tests where necessary.
• I have updated the documentation if required.
• I have built the package locally and run rebuilt docs using roxygen2.
• My code follows the established coding standards and I have run lintr::lint_package() to check for style issues introduced by my changes.
• I have added a news item linked to this PR.
• I have reviewed CI checks for this PR and addressed them as far as I am able.

[seabbs]

LGTM