[proxy] Implement compute node info cache (#3331)

This patch adds a timed LRU cache implementation and a compute node info cache on top of that.
Cache entries might expire on their own (default ttl=5mins) or become invalid due to real-world events,
e.g. compute node scale-to-zero event, so we add a connection retry loop with a wake-up call.

Solved problems:
- [x] Find a decent LRU implementation.
- [x] Implement timed LRU on top of that.
- [x] Cache results of `proxy_wake_compute` API call.
- [x] Don't invalidate newer cache entries for the same key.
- [x] Add cmdline configuration knobs (requires some refactoring).
- [x] Add failed connection estab metric.
- [x] Refactor auth backends to make things simpler (retries, cache
placement, etc).
- [x] Address review comments (add code comments + cleanup).
- [x] Retry `/proxy_wake_compute` if we couldn't connect to a compute
(e.g. stalled cache entry).
- [x] Add high-level description for `TimedLru`.

TODOs (will be addressed later):
- [ ] Add cache metrics (hit, spurious hit, miss).
- [ ] Synchronize http requests across concurrent per-client tasks
(https://github.com/neondatabase/neon/pull/3331#issuecomment-1399216069).
- [ ] Cache results of `proxy_get_role_secret` API call.

workspace_hack/Cargo.toml

@@ -25,6 +25,7 @@ futures-channel = { version = "0.3", features = ["sink"] }
 futures-executor = { version = "0.3" }
 futures-task = { version = "0.3", default-features = false, features = ["std"] }
 futures-util = { version = "0.3", features = ["channel", "io", "sink"] }
+hashbrown = { version = "0.12", features = ["raw"] }
 indexmap = { version = "1", default-features = false, features = ["std"] }
 itertools = { version = "0.10" }
 libc = { version = "0.2", features = ["extra_traits"] }
@@ -58,6 +59,7 @@ url = { version = "2", features = ["serde"] }
 anyhow = { version = "1", features = ["backtrace"] }
 bytes = { version = "1", features = ["serde"] }
 either = { version = "1" }
+hashbrown = { version = "0.12", features = ["raw"] }
 indexmap = { version = "1", default-features = false, features = ["std"] }
 itertools = { version = "0.10" }
 libc = { version = "0.2", features = ["extra_traits"] }