Support setting Puma worker count automatically

[sethboyles]

Puma 6.5.0 introduced this feature: puma/puma#3439

This feature apparently sets the number of Puma workers to the number of available processors detected.

Could be a handy if we supported this to ease the transition from Thin -> Puma

[stephanme]

I would like to keep the option for explicit configuration. Otherwise we lose the control over the CCDB connections needed per api VM. Currently, the max number of DB connections that an api VM can consume is puma.workers * puma.max_db_connections_per_process + 1 (+1 for the Puma main process).
DB connections becomes a critical size for PostgreSQL on large foundations with many CC VMs.

Maybe we can define that puma.workers = 0 means automatic worker count. Alternatively, an explicit option.