Allow override of docker image tag
Problem/Motivation
Currently the tag in the db/php service is set on "production", not allowing maintainers to switch to other tags for testing purposes
Steps to reproduce
Proposed resolution
Create a new variable DB/PHP_TAG or similar, with default value "production". I suggest doing this in core too.
That will allow testing with images other than drupalci, since all settings will be completely overrideable
Remaining tasks
User interface changes
API changes
Data model changes
Edited by drupalbot