Add XML conversion to bodies, and fix XML data conversion

[ySnoopyDogy]

The new XML validation functions just convert the data to JSON before validating the schema. With that, we can just convert the data on Request and Response validations just by looking at the content type.

Because in XML everything is a string, there can be problems to validating against a schema that includes other primitive types. Now, we convert the strings based on the schema types. If the property is a boolean, we convert to a boolean to pass the validation. If the value is not a valid boolean, we do nothing to let the schema validation to raise an error.

Also, now we are validating if the payload includes prefixes and namespaces defined in the schema (the XMLNS feature of XML).

Added a new option to ValidationOptions: AllowXMLBodyValidation to enable XML validations in request/response bodies (the default is false). Created a function WithXmlBodyValidation to enable the new validator option.

No breaking changes with the new code, as the updated function was internal, and the XML body validation setting is false by default.

[codecov]

Codecov Report

❌ Patch coverage is 98.14126% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.64%. Comparing base (0db7586) to head (09fe157).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
responses/validate_body.go	92.59%	2 Missing ⚠️
schema_validation/validate_xml.go	98.65%	2 Missing ⚠️
requests/validate_body.go	92.85%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #214      +/-   ##
==========================================
+ Coverage   97.61%   97.64%   +0.03%     
==========================================
  Files          56       57       +1     
  Lines        5240     5444     +204     
==========================================
+ Hits         5115     5316     +201     
- Misses        125      128       +3     

Flag	Coverage Δ
unittests	97.64% <98.14%> (+0.03%)	⬆️

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[ySnoopyDogy]

Going to implement a smarter conversion, like the one used in Query Parameter validation, looking to the type defined in the schema. This idea can be used to convert the body to JSON with correct defined types, so we can validate application/xml, x-www-form-urlencoded and also multipart/form-data