let update_synapse_database run on a multi-database configurations

[thefinn93]

The update_synapse_database script checks for the presence of the database key in the config. When multiple databases are used, the rest of synapse expects a different key, databases, which is mutually exclusive with database. this fixes the check to allow either key.

Pull Request Checklist

• [x] Pull request is based on the develop branch
• [x] 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.
• [x] Pull request includes a sign off
• [x] Code style is correct (run the linters)

[clokep]

Putting this back in the queue since I've lost all state on it and likely won't get to it soon.

[thefinn93]

yes, this change was tested and didn't seem to cause any issues