feat: ignore unrelated files in migration directory

[basti1302]

When the migration directory contains additional files, sql-migrations aborts with a rather cryptic error:

    ERROR: TypeError: Cannot read properties of null (reading '0')
        at /path/to/project/node_modules/sql-migrations/commands/run-migrations-command.js:36:43

The reason is twofold:

• migration-provider.js returns all files in the migration directory (the result of fs.readdir unconditionally and unfiltered.
• commands/run-migrations-command.js matches on the file name to extract the migration ID/timestamp and has no check if there is a match or not, it just uses the first match unconditionally.

This is especially annoying when working on migrations with editors that create a temporary file in the current directory, like vim does (vim automatically creates .1662812614706_up_my_migration.sql.swp when working on 1662812614706_up_my_migration.sql in the same directory). There might be other editors with similar behavior.

The fix in this change is also twofold:

• migration-provider.js now filters on files that end with .sql and will ignore other files. This might be debatable. Do people also use other file formats/suffixes? I am fine with dropping this change if you feel this is too restrictive.
• commands/run-migrations-command.js now checks if there is actually a match and prints a useful warning about the file that didn't match the expected pattern. Even with the first fix in migration-provider.js in place, this is still useful if there is an .sql file in the directory that does not match the expected file name pattern.