Add support for multiple configuration file locations

[blaz-kranjc]

Fixes #2735

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02 🎉

Comparison is base (ebc36a3) 90.96% compared to head (a29746c) 90.98%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3033      +/-   ##
==========================================
+ Coverage   90.96%   90.98%   +0.02%     
==========================================
  Files         160      160              
  Lines        3341     3351      +10     
  Branches      303      308       +5     
==========================================
+ Hits         3039     3049      +10     
  Misses        302      302              

Impacted Files	Coverage Δ
...g/scalasteward/core/repoconfig/RepoConfigAlg.scala	100.00% <100.00%> (ø)

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[mzuehlke]

Sorry for ignoring your PR for so long.
Thank you for your contribution.

[mkurz]

The .github and .config folder are both meant to be hidden (prefixed with a dot) and the .scala-steward.conf in the root folder is meant to be hidden as well.

Now, wouldn't it make sense to support a (non-hidden) scala-steward.conf within the .github and .config folder since both folder are hidden already?

E.g. look at how mergify does it (https://docs.mergify.com/configuration/)

Mergify uses the configuration file that is:

• The file named .mergify.yml, or, as a fallback, .mergify/config.yml or .github/mergify.yml from the root directory.

[mkurz]

Opened #3115