Use bitbucket static user for bitbucket git auth

[SantiarErhi]

Bitbucket App password will be disabled in 2.5 months (see https://www.atlassian.com/blog/bitbucket/bitbucket-cloud-enters-phase-2-of-app-password-deprecation). Since API token usage is inconsistent between bitbucket.org used for cloning repositories and api.bitbucket.org/2.0 used for working with PRs, etc (see https://support.atlassian.com/bitbucket-cloud/docs/using-api-tokens/), it's impossible to use API tokens with scala-steward and be able to clone a repository and read/write pull requests.

In order not to write another CLI option to specify another user for git or api, this solution uses static user name feature (see https://support.atlassian.com/bitbucket-cloud/docs/using-api-tokens/#Include-the-API-token-in-the-URL).

It works for me, but I'm not sure whether it's an appropriate solution.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.37%. Comparing base (e11ea69) to head (7599f18).
⚠️ Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
...ala/org/scalasteward/core/forge/BasicAuthAlg.scala	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3851      +/-   ##
==========================================
- Coverage   90.39%   90.37%   -0.02%     
==========================================
  Files         177      177              
  Lines        5110     5111       +1     
  Branches      458      422      -36     
==========================================
  Hits         4619     4619              
- Misses        491      492       +1     

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[SantiarErhi]

Bitbucket auth logic has been moved to separate class in order to not change logic for ALL ForgeTypes using BasicAuthAlg.