Add a warning for MeshExternalServices when mesh requirements are not met

[slonka]

Description

MeshExternalService requires:

• egress deployed (which requires mTLS and MeshTrafficPermissions)
• routing.zoneEgress: true (see bottom of https://kuma.io/docs/2.8.x/production/cp-deployment/zoneegress/#zone-egress)

would be nice to display a warning somewhere in MeshExternalServices tab if these requirements are not met

so something like this maybe could work:

On the user side when they are not met the MeshExternalService won't work and will error out with:

/app # wget -O- http://mes-https.extsvc.mesh.local/
Connecting to mes-https.extsvc.mesh.local ([::ffff:242.0.0.1]:80)
wget: error getting response: Connection reset by peer

Which is not very helpful, not sure we can do something there 🤔

[jakubdyszkiewicz]

It does not required routing.zoneEgress: true now. However, it requires mTLS