🚸 add configurable repo owner for mqt-core dependency

[burgholzer]

Description

This small PR adds a configuration option for the owner of the mqt-core dependency that is fetched via FetchContent. This should make it easier to point to forks of mqt-core.

Checklist:

• The pull request only contains commits that are related to it.
• I have added appropriate tests and documentation.
• I have made sure that all CI jobs on GitHub pass.
• The pull request introduces no new warnings and follows the project's style guidelines.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.4%. Comparing base (9a7fcf4) to head (8a14642).
Report is 83 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #482     +/-   ##
=======================================
- Coverage   90.4%   90.4%   -0.1%     
=======================================
  Files         86      86             
  Lines       9982    9982             
  Branches    1696    1696             
=======================================
- Hits        9027    9025      -2     
- Misses       955     957      +2     

Flag	Coverage Δ
cpp	90.1% <ø> (-0.1%)	⬇️
python	95.9% <ø> (ø)

see 1 file with indirect coverage changes