[docs] serviceAccount not used in example deployments

[kastl-ars]

In the quickstart section, a server and client deployment are being used.

Later, in the configuration section, ACLs are being shown that rely on serviceAccounts.

Unfortunately, the deployments are not using serviceAccounts, hence the examples are not working out of the box.

I created the service accounts and added the service accounts above the following lines (and adapted the namespaces, see #845) and the ACLs worked.

https://github.com/traefik/mesh/blob/638e27f9e29b8c6bdda214282d52bfc02fda94aa/docs/content/quickstart.md?plain=1#L77 https://github.com/traefik/mesh/blob/638e27f9e29b8c6bdda214282d52bfc02fda94aa/docs/content/quickstart.md?plain=1#L117

serviceAccountName: server

serviceAccountName: client