Support XDS HeaderMatcher string_match api (v3)

[jacob-delgado]

Use case(s) - what problem will this feature solve?

Allow the use of the match_string in envoyproxy/go-control-plane XDS support for gRPC clients. Currently, only the deprecated API is supported.

Proposed Solution

https://github.com/grpc/grpc-go/pull/5648

Alternatives Considered

None

Additional Context

This is preventing https://github.com/istio/istio/pull/40886 from getting merged for Istio.