feat: experimental support of OpenAPI 3.1

[Stranger6667]

Resolves #1820

[codecov]

Codecov Report

Merging #1823 (fbed84c) into master (3e2176c) will increase coverage by 0.07%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1823      +/-   ##
==========================================
+ Coverage   98.80%   98.88%   +0.07%     
==========================================
  Files         101      102       +1     
  Lines        8435     8487      +52     
  Branches     1758     1767       +9     
==========================================
+ Hits         8334     8392      +58     
+ Misses         59       57       -2     
+ Partials       42       38       -4     

Files	Coverage Δ
src/schemathesis/cli/__init__.py	99.25% <100.00%> (+<0.01%)	⬆️
src/schemathesis/cli/callbacks.py	100.00% <100.00%> (ø)
src/schemathesis/cli/output/default.py	99.23% <100.00%> (+0.01%)	⬆️
src/schemathesis/experimental/__init__.py	100.00% <100.00%> (ø)
src/schemathesis/specs/openapi/loaders.py	98.81% <100.00%> (+0.02%)	⬆️
src/schemathesis/specs/openapi/schemas.py	98.80% <100.00%> (+<0.01%)	⬆️

... and 4 files with indirect coverage changes