GHSA-hrxh-6v49-42gf: gRPC-Go: xDS RBAC and HTTP/2 Vulnerabilities

Multiple security vulnerabilities have been identified and addressed in grpc-go affecting the xDS RBAC authorization engine (internal/xds/rbac) and the HTTP/2 transport server implementation (internal/transport). These vulnerabilities could result in:

• Authorization Bypass (Fail-Open) when translating xDS RBAC policies containing Metadata or RequestedServerName fields.
• Denial of Service (High CPU Consumption) due to an HTTP/2 Rapid Reset mitigation bypass during client-initiated stream resets.
• Denial of Service (Server Panic) when parsing crafted xDS RBAC policies containing NOT rules around unsupported fields.