Implement OAuth 2.0 Protected Resource Metadata

[jgrandja]

Add support for OAuth 2.0 Protected Resource Metadata.

See the following integration test on how to customize the metadata response:

spring-security/config/src/test/java/org/springframework/security/config/annotation/web/configurers/oauth2/server/resource/OAuth2ProtectedResourceMetadataTests.java

Line 113 in 54aae36

public void requestWhenProtectedResourceMetadataRequestAndMetadataCustomizerSetThenReturnCustomMetadataResponse()

[jochenchrist]

This feature is required for MCP Server OAuth authentication: https://modelcontextprotocol.io/specification/2025-06-18/basic/authorization#authorization-server-location