proxy: Changes to rate limits and GetEndpointAccessControl caches. (#12048)

Precursor to https://github.com/neondatabase/cloud/issues/28333.

We want per-endpoint configuration for rate limits, which will be
distributed via the `GetEndpointAccessControl` API. This lays some of
the ground work.

1. Allow the endpoint rate limiter to accept a custom leaky bucket
config on check.
2. Remove the unused auth rate limiter, as I don't want to think about
how it fits into this.
3. Refactor the caching of `GetEndpointAccessControl`, as it adds
friction for adding new cached data to the API.

That third one was rather large. I couldn't find any way to split it up.
The core idea is that there's now only 2 cache APIs.
`get_endpoint_access_controls` and `get_role_access_controls`.

I'm pretty sure the behaviour is unchanged, except I did a drive by
change to fix #8989 because it felt harmless. The change in question is
that when a password validation fails, we eagerly expire the role cache
if the role was cached for 5 minutes. This is to allow for edge cases
where a user tries to connect with a reset password, but the cache never
expires the entry due to some redis related quirk (lag, or
misconfiguration, or cplane error)

libs/utils/src/leaky_bucket.rs

@@ -28,6 +28,7 @@ use std::time::Duration;
 use tokio::sync::Notify;
 use tokio::time::Instant;
 
+#[derive(Clone, Copy)]
 pub struct LeakyBucketConfig {
     /// This is the "time cost" of a single request unit.
     /// Should loosely represent how long it takes to handle a request unit in active resource time.