When vector axiom sink changes merge, update our connectivity docs for vector accordingly

[darach]

We raised an issue ( vectordotdev/vector#21292 ) with the vector project
to switch out the elasticsearch backend to the vector axiom sink with our native ingest endpoint.

When the PR ( vectordotdev/vector#21362 ) passes approvals, checks and is merged, we need to make the requisite changes to our own documentation.

Once this rolls into a vector release we can update our docs and publicise the change to our vector
users in turn.