router: allow matching on gRPC requests (#4401)
router: allow matching on gRPC requests (#4401)

This adds the option to match on gRPC requests directly instead of
indrectly doing so through header matchers. It provides a more robust
matching mechanism, as it incorporates the gRPC content-type variations
into the check.

Signed-off-by: Snow Pettersen <snowp@squareup.com>

Mirrored from https://github.com/envoyproxy/envoy @ 701618f65a7513e2453d04ff1bc5cb2cc864c401

lyft/envoy-api,lyft/envoy-api,lyft/envoy-api