Add GitLab CI/CD configuration for quest packaging

This enables the new Solarus Devops quest packaging pipelines for ZSDX.

Once added, the pipelines will create packages:

1. At each commit with packages named zsdx-<COMMIT_HASH>.solarus
2. At each tag with packages named zsdx-<TAGNAME>.solarus

These are directly accessible using URLs with the following form:

https://gitlab.com/solarus-games/zsdx/-/jobs/
    artifacts/<ref>/raw/<path_to_file>?job=<job_name>

Where (depending if commit-based or tag-based):

• <ref> is dev or TAGNAME
• <path_to_file> is zsdx-<COMMIT_HASH>.solarus or zsdx-<TAGNAME>.solarus
• <job_name> is quest-package or quest-rel-package

Resolves #134 (closed)