/flags go live checklist

[dmarticus]

The /flags endpoint is ready for big time – with these PRs (#33194, #33032) landing, we now support all of the /decide fields on /flags, which means we can cut over to /flags with no loss of functionality. Putting together a launch checklist:

Infra

• Scale up the posthog-feature-flags service in US and EU to 140 HPA per datacenter #33327
• Clean up the logging in the /flags service #33264
• Once-over on the flags metrics #33328

SDKs

• Roll out /flags to posthog-js feat(flags): replace /decide with /flags&config=true posthog-js#2000. NB: make sure I'm hashing the token rollout initially so that it only goes to a subset of traffic since JS changes often propagate immediately.
• Roll out /flags to android use /flags instead of /decide posthog-android#245
• Roll out /flags to iOS chore(flags): use new /flags endpoint instead of /decide posthog-ios#345
• Clean up the excluded tokens from Python and Node #33331

Docs

• Update all references to /decide in our docs to talk about /flags or /flags&config=true #33329

[dmarticus]

gonna add the post-launch checklist to a different ticket, since it's not a priority and I'd like to see how things are looking before I look into this too much.