feat: allow multiple themes

Description

This MR adds ability to define, build, and deploy multiple themes. If a theme sets the DEFAULT to true, that team will be considered as the default theme and enabled. If no themes are setting the DEFAULT key to true, the first theme in the list is considered to be the default one.

Non-default themes can be set using custom site settings from the admin site of the instance.

Supporting information

https://tasks.opencraft.com/browse/SE-5956

Testing instructions

Steps to test the changes:

1. Check that pipeline https://gitlab.com/opencraft/ops/grove-stage-aws/-/pipelines/867812114 is succeeded
2. In the logs of https://gitlab.com/opencraft/ops/grove-stage-aws/-/jobs/4287255572 search for simple-theme-default and simple-theme-secondary
3. Check that the default theme is provided for the settheme command in https://gitlab.com/opencraft/ops/grove-stage-aws/-/jobs/4287255574#L1568

Dependencies

N/A

Screenshots

See the list of available themes within the pod:

Checklist

If any of the items below is not applicable, do not remove them, but put a check in it.

• All providers include the new feature/change
• All affected providers can provision new clusters
• Unit tests are added/updated
• Documentation is added/updated
• The TOOLS_CONTAINER_IMAGE_VERSION in ci_vars.yml is updated
• The grove-template repository is updated

Additional context

Defining several themes have effect on the build time.