[Deprecations] Deprecate SQLite Migrations

[quaark]

https://iguazio.atlassian.net/browse/ML-5884

We still support SQLite as a DB, but no longer do we support upgrading the SQLite DB with alembic migrations. Now migrations are only for MySQL:

• Removed sqlite migrations and models file
• API only runs migrations if DB engine is mysql
• Move migration tests to test against mysql and not sqlite (removed 3 tests that are no longer relevant as those migrations are before the init migration of mysql)
• Added migration with missing changes from mysql db
• Update mysql collation from utf8_bin to utf8mb3_bin. utf8_bin is deprecated in MySQL and now uses utf8mb3_bin when utf8_bin is set. Alembic tries to migrate the db back to utf8_bin but shouldn't. Now the collation in code matches MySQL collation. TODO: upgrade to utf8mb4_bin in the future as described in the MySQL warning.

2024-05-28 11:29:05 2024-05-28T08:29:05.147254Z 0 [Warning] [MY-013242] [Server] --character-set-server: 'utf8' is currently an alias for the character set UTF8MB3, but will be an alias for UTF8MB4 in a future release. Please consider using UTF8MB4 in order to be unambiguous.
2024-05-28 11:29:05 2024-05-28T08:29:05.147580Z 0 [Warning] [MY-013244] [Server] --collation-server: 'utf8mb3_bin' is a collation of the deprecated character set UTF8MB3. Please consider using UTF8MB4 with an appropriate collation instead.