Return allowed CORS headers in the letter case they were submitted in and update the test

[sberyozkin]

Fixes #16208

This PR updates the CORS test checking that if quarkus.http.cors.headers property matches the headers provided in the CORS request then a correct list of headers will be returned.

Additionally, a minor update to the CORS filter was made to ensure the letter case is preserved, example, if the browser sends Access-Control-Request-Headers: x_custom and Quarkus approves it using its case-insensitive headers match, then it should get back Access-Control-Allowed-Headers: x_custom, not Access-Control-Allowed-Headers: X_CUSTOM, the same with content-type vs CONTENT-TYPE as either the browser or Quarkus can have a lower-case or upper-case header value provided/configured

[quarkus-bot]

Failing Jobs - Building bd521fc

Status	Name	Step	Failures	Logs	Raw logs
✔️	JVM Tests - JDK 11
✔️	JVM Tests - JDK 17
✖	JVM Tests - JDK 17 MacOS M1	Set up runner	⚠️ Check →	Logs	Raw logs
✔️	JVM Tests - JDK 18