fix: Allow relative references in all URLs

[jtv8]

Following up from #618 - this doesn't quite bring the library into compliance with the spec yet as this rule applies to all URLs.

https://swagger.io/specification/#relative-references-in-urls

Relative References in URLs
Unless specified otherwise, all properties that are URLs MAY be relative references as defined by RFC3986. Relative references are resolved using the URLs defined in the Server Object as a Base URI.

There aren't (as of 3.0.3) any exceptions defined to this, so this PR removes all uses of AnyUrl and replaces them with str.

[dbanty]

Awesome, thanks!

[codecov]

Codecov Report

Merging #630 (71ffef2) into main (82a9ad6) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #630   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           49        49           
  Lines         1713      1713           
=========================================
  Hits          1713      1713           

Impacted Files	Coverage Δ
...n_client/schema/openapi_schema_pydantic/contact.py	100.00% <100.00%> (ø)
.../openapi_schema_pydantic/external_documentation.py	100.00% <100.00%> (ø)
...thon_client/schema/openapi_schema_pydantic/info.py	100.00% <100.00%> (ø)
...n_client/schema/openapi_schema_pydantic/license.py	100.00% <100.00%> (ø)
...lient/schema/openapi_schema_pydantic/oauth_flow.py	100.00% <100.00%> (ø)
.../schema/openapi_schema_pydantic/security_scheme.py	100.00% <100.00%> (ø)

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