This PR does the following things:
* The initial heartbeat round blocks the storage controller from
becoming online again. If all safekeepers are unresponsive, this can
cause storage controller startup to be very slow. The original intent of
#10583 was that heartbeats don't affect normal functionality of the
storage controller. So add a short timeout to prevent it from impeding
storcon functionality.
* Fix the URL of the utilization endpoint.
* Don't send heartbeats to safekeepers which are decomissioned.
Part of https://github.com/neondatabase/neon/issues/9011
context: https://neondb.slack.com/archives/C033RQ5SPDH/p1739966807592589
Preparations for a successor of #10440:
* move `pull_timeline` to `safekeeper_api` and add it to
`SafekeeperClient`. we want to do `pull_timeline` on any creations that
we couldn't do initially.
* Add a `SafekeeperGeneration` type instead of relying on a type alias.
we want to maintain a safekeeper specific generation number now in the
storcon database. A separate type is important to make it impossible to
mix it up with the tenant's pageserver specific generation number. We
absolutely want to avoid that for correctness reasons. If someone mixes
up a safekeeper and pageserver id (both use the `NodeId` type), that's
bad but there is no wrong generations flying around.
part of #9011
In #9011, we want to schedule timelines to safekeepers. In order to do
such scheduling, we need information about how utilized a safekeeper is
and if it's available or not.
Therefore, send constant heartbeats to the safekeepers and try to figure
out if they are online or not.
Includes some code from #10440.
Avoids compiling the crate and its dependencies into binaries that don't
need them. Shrinks the compute_ctl binary from about 31MB to 28MB in the
release-line-debug-size-lto profile.
Add an endpoint to obtain the utilization of a safekeeper. Future
changes to the storage controller can use this endpoint to find the most
suitable safekeepers for newly created timelines, analogously to how
it's done for pageservers already.
Initially we just want to assign by timeline count, then we can iterate
from there.
Part of https://github.com/neondatabase/neon/issues/9011
## Problem
We want to use safekeeper http client in storage controller and
neon_local.
## Summary of changes
Extract it to separate crate. No functional changes.
