refactor: New validator package (from #959) to simplify code in the following PRs

[dadrus]

Related issue(s)

none.

Checklist

• I agree to follow this project's Code of Conduct.
• I have read, and I am following this repository's Contributing Guidelines.
• I have read the Security Policy.

Description

Cherry picking the new validation package from #956 to have the functionality in the main branch and being able to simplify the code base independent from the above said PR

[codecov]

Codecov Report

Merging #962 (f3f113b) into main (c7a8af3) will not change coverage.
Report is 2 commits behind head on main.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #962   +/-   ##
=======================================
  Coverage   89.82%   89.82%           
=======================================
  Files         234      234           
  Lines        9650     9650           
=======================================
  Hits         8668     8668           
  Misses        762      762           
  Partials      220      220           

Files	Coverage Δ
...mechanisms/authenticators/generic_authenticator.go	92.21% <100.00%> (ø)
...les/mechanisms/authenticators/jwt_authenticator.go	92.32% <100.00%> (ø)
...thenticators/oauth2_introspection_authenticator.go	89.92% <100.00%> (ø)

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