Add .gitlab-ci.yml

Once the issues reported by gitlab-ci are resolved, we'll need to update the .gitlab-ci.yml file with something like this (see example):

#
# Linting jobs are passing so any issue that breaks them should fix them.
#
cspell:
  allow_failure: false
eslint:
  allow_failure: true
phpcs:
  allow_failure: false
phpstan:
  allow_failure: false
stylelint:
  allow_failure: false

Results here https://git.drupalcode.org/issue/commerce_wishlist-3432043/-/pipelines/1...

Merged the MR.

Automatically closed - issue fixed for 2 weeks with no activity.