fix(sqlite): do NOT create two db connections

[Weakky]

Fixes https://github.com/prisma/prisma-engines/issues/1481

This removes support for the path params "db_name". Quaint was using the ATTACH DATABASE statement as a hack to scope the db under some custom name. The ATTACH DATABASE statement is initially designed to create another connection to a different db so that one can query multiple dbs. This was causing subtle issues with transactions.

Namely, if inside a transaction, a user would "manually" execute (with executeRaw) a write without prefixing the tables with the custom db name (using one connection), and that the QE would also execute a read, this time with the tables prefixed with the db_name (therefore with another connection), this would cause two different connections attempting to do READ/WRITES inside a transaction, causing locks as explained in this doc https://sqlite.org/isolation.html

SQLite has as default db name, it's called main. This PR defaults the db_name to main. This enables:

• The QE to keep referring to the tables using some alias (main)
• The users to refer to their tables without using any aliases (that they're not aware of anyway). This is possible because when no alias is used, SQLite will default to using the main connection.

[Weakky]

Great, did you test this in Prisma engines already?

When merging, remember to squash.

I did, it works. It actually works even without this fix since the QE fix no longer passes the db_name params anyway, so the attach db stuff is no longer called. PR's here, I just need to add a simple test https://github.com/prisma/prisma-engines/pull/1644