[PECO-1436] [sqlalchemy] Include sqlalchemy __version__ in user-agent

[susodapop]

Description

This pr updates our user-agent setting logic for the sqlalchemy dialect so that we include the sqlalchemy package version.

I used this as an opportunity to reorganise the two (now three) user agent tests into their own test class.

Here's an example of how it's recorded in the query history:

[susodapop]

I'm double-checking the correct format. Will hold off on merging this until next week.