Consolidate `dbtype-commands.txt` files for easier maintainability

As a next step to #471, move the commands that are common to all database types to a common file.

Benefits in performing this:

1. This ensures that changes have to be made at only one place
2. Latest updates to config files will be reflected across all SQL database types.

Start by locating every dbtype-commands.txt file in the repository and compare the commands across the SQL database types. Identify which commands are common and determine how each database configuration references them. Done means common commands are maintained in one shared file and updates are reflected across all SQL database configurations.

Vom Indexierungsmodell aus dem Issue-Text verfasst.