[SE-5478] feat: add build image pipeline

Description

This PR adds a new pipeline to Grove allowing us to pre-build images based on commits.

Test instructions

lt;dr:

1. validate that https://gitlab.com/opencraft/ops/grove-stage-digitalocean/-/jobs/2351004330 succeeds
2. check that a maple.3 image exists at https://gitlab.com/opencraft/ops/grove-stage-digitalocean/container_registry/2967280

longer version:

0. set TOOLS_CONTAINER_IMAGE_VERSION to gabor-add-image-build-pipeline
1. in the DO staging environment, checkout this branch
2. change someting or amend the latest commit using [AutoDeploy][Build][Image] https://github.com/edx/edx-platform.git|open-release/lilac.3
3. push the changes and check a new pipeline started to build the image
4. validate the job succeeds and the image is uploaded to the container registry
5. revert the grove version changes in the staging cluster repo

Documentation

Author notes

This PR contains some additional changes too:

1. Reformatted the code using make format
2. Added a -v flag to the pytest command to have more meaningful test failure messages