Host `mappingSelector` should apply also to `TCPMapping`

[blacksd]

Please describe your use case / problem. Currently a Host can define a mappingSelector to allow a Mapping with the appropriate label to select automatically the corresponding Host.

apiVersion: getambassador.io/v3alpha1
kind: Host
metadata:
  name: api
  namespace: emissary-system
spec:
  hostname: api.my-domain.com
  tlsSecret:
    name: bogus-api-cert-secret
    namespace: cert-manager
  mappingSelector:
    matchLabels:
      emissary-host: api
---
apiVersion: getambassador.io/v3alpha1
kind: Mapping
metadata:
  name: podinfo-default-get
  namespace: test-podinfo
  # Use a label to allow a Host to select this Mapping
  labels:
    emissary-host: api
spec:
  prefix: /
  method: GET
  service: http://frontend-podinfo:9898

This doesn't apply to TCPMapping though; if a TCPMapping is configured with a label that could allow it to select a Host, that Host isn't selected automatically and a generic default Listener is created in its place.

apiVersion: getambassador.io/v3alpha1
kind: Host
metadata:
  name: ingest
  namespace: emissary-system
spec:
  hostname: ingest.my-domain.com
  tlsSecret:
    name: bogus-ingest-cert-secret
    namespace: cert-manager
  mappingSelector:
    matchLabels:
      emissary-host: ingest
---
apiVersion: getambassador.io/v3alpha1
kind: TCPMapping
metadata:
  name: go-echo-default
  namespace: test-go-echo
  labels:                 # <-- does not
    emissary-host: ingest # <-- work
spec:
  port: 6443
  service: tcp-echo-service:2701

Describe the solution you'd like

I would like to be able to define a Host and mappingSelector as usual, but allow a TCPMapping with the appropriate label to select automatically the matching Host.

Describe alternatives you've considered

The only solution other than leaving the host selection as is, would rely on creating either a separate selector (tcpMappingSelector). I'm not sure about the practical implications or the effectiveness of this implementation proposal.

Additional context

N/A