Allow injecting bootstrap info into xDS Filter API for config parsing

[sauravzg]

This sits on top of #12492 , so please view the commits after it.

Extend the xDS Filter API to support injecting bootstrap information into
filters during configuration parsing. This allows filters to access context
information (e.g., allowed gRPC services) from the resource loading layer
during configuration validation and parsing.

• Update Filter.Provider.parseFilterConfig and parseFilterConfigOverride
  to accept a FilterContext parameter.
• Introduce BootstrapInfoGrpcServiceContextProvider to encapsulate
  bootstrap info for context resolution.
• Update XdsListenerResource and XdsRouteConfigureResource to
  construct and pass FilterContext during configuration parsing.
• Update sub-filters (FaultFilter, RbacFilter, GcpAuthenticationFilter,
  RouterFilter) to match the updated FilterContext signature.

Known Gaps & Limitations:

1. MetricHolder: Propagation of MetricHolder is not supported with
   this approach currently and is planned for support in a later phase.
2. NameResolverRegistry: Propagation is deferred for consistency. While
   it could be passed from XdsNameResolver on the client side, there is
   no equivalent mechanism on the server side. To ensure consistent behavior,
   DefaultRegistry is used when validating schemes and creating channels.

[sauravzg]

@kannanjgithub @AgraVator PTAL and add yourself as reviewers on the PR. Thanks.

[sauravzg]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a new parser for the external authorization (ExtAuthz) filter and a comprehensive GrpcService configuration parser within the xDS implementation. It refactors the Filter interface to include a FilterContext during configuration parsing, enabling filters to access bootstrap and server-specific metadata. The changes also enhance the bootstrap process to support allowed_grpc_services and add various internal configuration classes for header mutation and validation. Feedback was provided to replace unchecked UnsupportedOperationException calls with checked GrpcServiceParseException instances in the GrpcServiceConfigParser to ensure that unsupported credential types result in a validation error (NACK) rather than crashing the xDS client thread.