Validate the Puma performance pattern for different memory configurations

Extending the https://gitlab.com/gitlab-org/gitlab-ce/issues/62876 we should validate the Puma performance in memory-constrained environments:

1. We should investigate how memory-constrained environments affect RPS,
2. We should investigate how increased GC pressure affects RPS,
3. We should understand how Puma Memory Killer affects RPS (should we lower or make this setting higher).

Expectations:

1. We should have a clear guideline of how the available memory affects the given configuration of Puma (worker/threads),
2. We should have a proposal for default Puma Memory Killer values that should be put as our defaults,
3. We should have a proposal for worker/threads configuration of Puma for: a. low-performance environments (slow CPUs), b. low memory environments.

As a result:

1. We should have Omnibus MR that resolves the omnibus-gitlab#3896 (closed),
2. Update our documentation guidelines.

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/62877, omnibus-gitlab#3896 (closed).