feat: update submodules and add dependabot for the future

Description

Updates both ckanext-zarr and ckanext-fjelltopp-theme to latest default branches in preparation of a staging deploy.

Also adds dependabot so that this should be a bit more automated moving forwards.

[ ] The GitHub ticket for this issue has been updated to "Ready to Review" or equivalent.
[x] I have developed these changes in discussion with the appropriate project manager.
[x] My code follows the general Fjelltopp documentation (see Confluence).
[ ] I have made corresponding changes to the Fjelltopp documentation (see Confluence).
[x] I have rebased this branch with master.
[x] New dependency changes have been committed.
[ ] I have added automated tests that prove my fix is effective or that my feature works.
[x] New and existing tests pass locally with my changes.
[x] My changes generate no new warnings.
[x] I have performed a self-review of my own code.
[x] I have assigned at least one reviewer.
[x] I have assigned at least one label to this PR: "patch", "minor", "major".