We want to switch away from and deprecate the `--compute-hook-url` param
for the storcon in favour of `--control-plane-url` because it allows us
to construct urls with `notify-safekeepers`.
This PR switches the pytests and neon_local from a
`control_plane_compute_hook_api` to a new param named
`control_plane_hooks_api` which is supposed to point to the parent of
the `notify-attach` URL.
We still support reading the old url from disk to not be too disruptive
with existing deployments, but we just ignore it.
Also add docs for the `notify-safekeepers` upcall API.
Follow-up of #11173
Part of https://github.com/neondatabase/neon/issues/11163
b1a1be6a4c