Process headers to ensure compatibility between legacy and netty validation

[mrsaldana]

• I have considered the risk of behavior change or other zero migration impact (https://github.com/OpenLiberty/open-liberty/wiki/Behavior-Changes).
• If this PR fixes an Issue, the description includes "Fixes #FILLMEIN" or "Resolves #FILLMEIN" (verify release bug label if applicable: https://github.com/OpenLiberty/open-liberty/wiki/Open-Liberty-Conventions).
• If this PR resolves an external Known Issue (including APARS), the description includes "Fixes #FILLMEIN" or "Resolves #FILLMEIN".

This PR introduces a HeaderValidator utility class for validating HTTP header names and values. Validation is made to comply with RFC 7230, Section 3.2. This RFC refers to "HTTP/1.1 Message Syntax and Routing" and Section 3.2 covers "Header Fields". In addition to enforcing strict checks to ensure the header is compliant, the utility normalizes the tokens by stripping whitespace padding and lower-casing header field names.

Testing

The accompanying unit tests confirm expected behaviors on:

• Header name validation
• Header value validation
• Length validation
• Null input handling
• Header field normalization

Usage

String headerName = HeaderValidator.process("Content-Type", FieldType.NAME, config);
String headerValue = HeaderValidator.process(" application/json ", FieldType.VALUE, config);
// Normalized headerName: "content-type"
// Normalized headerValue: "application/json"

[mrsaldana]

Enhancements for translating warning messages on validator will be resolved by #30653

[isaacrivriv]

This looks good to me, thanks!!