Upgrade Puma to v5.1

We need to update to the latest Puma to use nakayoshi_fork (https://msp-greg.github.io/puma/Puma/DSL.html#nakayoshi_fork-instance_method).

When enabled, ::Puma will GC 4 times before forking workers. If available (Ruby 2.7+), we will also call GC.compact.

Additionally, we'll benefit from using the actual version of the library.

Before applying any v5-related features (like nakayoshi_fork) it would be important to make sure v5 is stable in production and check if it brings some difference in CPU/Mem usage as it is.

Rollout sequence (to be updated)

• Bump the gem version and check if the CI is green
• Check how we updated to Ruby 2.7, it may be a similar strategy
• Communicate with #g-delivery - they suggested regular rollout with sync communication
• Discuss with SRE if need to do a flagged/ENV-var-ed rollout, or just a regular is enough - regular is
• Go through list of Puma 5 breaking changes: !48897 (merged)
• Get approvements on all MRs: CNG/Omnibus/GitLab
• Coordinate CNG/Omnibus/GitLab MRs merges with #g-delivery
• Rollout: may be a separate issue when we get there, monitor on Canary before going live

Related to #288042 (closed)