Reduce false-positives when detecting SQLite usage

[SamWheating]

While working on a different fix I noticed that we were checking for sqlite like so:

if 'sqlite' in conf.get('core', 'sql_alchemy_conn')

While I know that its unlikely, this could incorrectly detect sqlite if the string appears anywhere in the sqlalchemy connection string. For example, a postrges connection to a database called not-sqlite:

postgresql://user:pass@localhost:5432/not-sqlite

Anyways, using .startswith('sqlite') should be a little more reliable here, as the dialect is always specified at the very beginning of an sqlalchemy connection string.

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