Resolve "Let DataManager path matching work with multiple matches"

This MR generalizes and cleans up the target path creation method in DataManager.

• Adds new ext and dirname format string keys
• Adds new groups and named keys, giving access to all matches
• Removes an overly pedantic error message (upon missing match in format string)
• Delays the error message for warning about a failing format operation to the point where all information is available.

Can this MR be accepted?

• Implementation ready
• Tests added or adjusted
• Documentation extended or updated

• Code quality
  • Changes follow coding guidelines
  • Checked code coverage on new and adjusted code

• Ready for merging
  • Pipeline passes without warnings
  • History cleaned-up or squash option set
  • Changelog entry added
  • Version number bumped

Related issues

Closes #206 (closed)