Subscription checking

[darh]

Check subscription (at permit.crust.tech) on runtime and on intervals (every 24h, starting on startup).

We'll enhance this with softer (UI) warnings, emails etc later.

Todo:

• Check on startup -- refuse to start; shutdown (for now) and log if subscription expired.
  • on system service
  • on messaging service
  • on crm/compose service
  • on cmd/crust (monolith)
• Check every 24h.

On each check, send some statistics to subscription server:

• messaging (number of public, private channels)
• system (number of organisations, teams, users)
• crm (number of modules, number of pages, number of records)