Re-add ability to create db if it did not exist

[pierlon]

Removing the ability to create the WordPress database on container startup has broken environments that rely on that feature (see WordPress/gutenberg#29752 and ampproject/amp-wp#5974 as examples). Because of this change users relying on this image will now have to customize the image to add tools such as wait-for-it so that the container will wait on their MySQL container provision the database.

I'm not sure why this feature has been removed as there are no commits or comments explaining the need for the change, but I do hope this PR is accepted so that users of the image won't have to wake up to a broken environment 😄.

[pierlon]

I suppose the change was in relation to not attempting to create the DB if not desired. In 9bd1b97 I've added a new env var called SKIP_DB_CREATION that will skip the attempt to create the DB.

[yosifkit]

Copying over my comment:

Creating the database should not have been the job of the WordPress container since that means the database user has more access than it needs to store WordPress data.

Both the mysql and mariadb images have support for creating a database and user with limited access (as is done in the example WordPress stack.yml here)

[pierlon]

Understood. Thanks for the clarification and updating the related docs.