Sentry Alert configuration based on production and development environment

[zeeshanrafiqrana]

Pull Request Checklist

• Pull request is based on the develop branch
• Pull request includes a changelog file. The entry should:
  • Be a short description of your change which makes sense to users. "Fixed a bug that prevented receiving messages from other servers." instead of "Moved X method from EventStore to EventWorkerStore.".
  • Use markdown where necessary, mostly for code blocks.
  • End with either a period (.) or an exclamation mark (!).
  • Start with a capital letter.
  • Feel free to credit yourself, by adding a sentence "Contributed by @github_username." or "Contributed by [Your Name]." to the end of the entry.
• Pull request includes a sign off
• Code style is correct
  (run the linters)

[zeeshanrafiqrana]

Issue Associated with this PR: Sentry Alert configuration based on production and development environment

[erikjohnston]

(Sign off has been completed out-of-band)

[erikjohnston]

Thanks! Sorry, I've missed the fact that'll you need to:

1. add a changelog file (as per the contributing guide); and
2. add a brief description of the new option at https://github.com/matrix-org/synapse/blob/10ada2ff6d2a08108edf5b4dbe6562cc9465523d/docs/usage/configuration/config_documentation.md#sentry

Hopefully that should only take ten minutes.

[erikjohnston]

I've updated the wording a little bit to match our style, but they're only minor tweaks,

Thanks for your contribution!