Add RPC functions to install/update SQL on configured databases

[mathemancer]

Fixes #4017

This adds an RPC function, databases.upgrade_sql. It's documented as usual, and the documentation should suffice to describe its use.

It also adds some attributes to the Database model and exposes them in databases.configured.list:

• last_confirmed_sql_version: The last version of the SQL scripts which were confirmed to have been run on the database.
• needs_upgrade_attention: This is True if the SQL version isn't confirmed to be the same as the service version.

Technical details

The function will automatically determine the correct role to use for the upgrade if a username and password aren't submitted. If they are submitted, then the function will attempt to use the specified role.

This PR also includes some general clean up and simplification of our installation code.

Screenshots

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[Anish9901]

LGTM! Just a minor suggestion.