PRR: Set educated limits for per-instance concurrent requests

[raserva]

Currently, lumberjack terraform sets the instance type (1G memory, 1 CPU) and uses the defaults for Cloud Run scaling.

By default each Cloud Run container instance can receive up to 80 requests at the same time

We should understand whether the lumberjack ingestion service can handle 80 concurrent requests with the specified instance type, or if this should be set differently.