Update the service mesh integration docs to explain how Consul needs to be
configured for transparent proxy. Update the walkthrough to assume that
`transparent_proxy` mode is the best approach, and move the manually-configured
`upstreams` to a separate section for users who don't want to use Consul DNS.
Ref: https://github.com/hashicorp/nomad/pull/20175
Ref: https://github.com/hashicorp/nomad/pull/20241
* docs: move CNI reference plugins installation to CNI overview page
This PR moves the instruction steps for install the CNI reference plugins
from the Consul Mesh integration page to the general Networking CNI page.
These plugins are required for bridge networking, not just Consul Mesh,
so it makes sense to have them on the general CNI page.
Closes#17038
* docs: fix a link to post install steps
