refactor: use slices.Contains instead of for loop to check if the provided db is in AllowedDBDrivers

[sajjadvaezi]

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

Problem/Feature

Description of Changes:

• use slices.Contains instead of for loop to check if the provided db is in AllowedDBDrivers

Checklist

• I have self-reviewed the changes being requested
• I have updated the documentation (check issue ticket 📋Update documentation if the PR introduces a new feature!📋 #218)

[Ujstor]

I am not sure what the purpose of the PR is. You changed only one file in the flags dir, and the tests are failing.

I will close it as incomplete.