[docs] Teleport Connect Kube gateway v14 update

[greedy52]

Related change:

• Connect Kube gateway part 4: frontend #29376

Closes #26836

[ravicious]

The changes to the docs address the change in the underlying implementation well. I added a couple of suggestions on how to make the docs even more clear.

[ravicious]

Suggested change

	A new local terminal tab will open with a new connection to the specified
	cluster, and the terminal will be preconfigured with the `$KUBECONFIG`
	environment variable pointing to a configuration for this specified cluster. Any
	A new local terminal tab will open with the `$KUBECONFIG`
	environment variable pointing to a configuration for this specified cluster. Any

I'm not sure if it's worth mentioning the connection. For database gateways, we use the gateway tab to represent that "connection", we say "Database Connection" at the top of the tab. For kube gateways, such tab doesn't exist, you jump into the terminal directly.

In that case, from the user's point of view there's no "connection". But also the concept of a connection itself doesn't help the user with understanding how this feature works. If anything, we could mention that this is the equivalent of running tsh proxy kube, but I don't think it's absolutely necessary.

[greedy52]

I removed reference to connection and rewrote the last paragraph a little bit. Not sure if it's clear enough or anything is missing. Could you take another look? Thanks!