## Problem
In Neon DBaaS we adjust the shared_buffers to the size of the compute,
or better described we adjust the max number of connections to the
compute size and we adjust the shared_buffers size to the number of max
connections according to about the following sizes
`2 CU: 225mb; 4 CU: 450mb; 8 CU: 900mb`
[see](877e33b428/goapp/controlplane/internal/pkg/compute/computespec/pg_settings.go (L405))
## Summary of changes
We should run perf unit tests with settings that is realistic for a
paying customer and select 8 CU as the reference for those tests.
## Problem
Endpoint kept running while timeline was deleted, causing forbidden
warnings on the pageserver when the tenant is not found.
## Summary of changes
- Explicitly stop the endpoint before the end of the test, so that it
isn't trying to talk to the pageserver in the background while things
are torn down
Adds a benchmark for logical message WAL ingestion throughput
end-to-end. Logical messages are essentially noops, and thus ignored by
the Pageserver.
Example results from my MacBook, with fsync enabled:
```
postgres_ingest: 14.445 s
safekeeper_ingest: 29.948 s
pageserver_ingest: 30.013 s
pageserver_recover_ingest: 8.633 s
wal_written: 10,340 MB
message_count: 1310720 messages
postgres_throughput: 715 MB/s
safekeeper_throughput: 345 MB/s
pageserver_throughput: 344 MB/s
pageserver_recover_throughput: 1197 MB/s
```
See
https://github.com/neondatabase/neon/issues/9642#issuecomment-2475995205
for running analysis.
Touches #9642.
