feat: improve demo data to include TRG insitutes and group icons

Description

Improves the demo data to include all the TRG institutes and one admin per institute.

Also adds images to the groups for visualising on the home page.

relates (but is not dependent on) fjelltopp/ckanext-zarr#44

Submodules will need updating before merging (but after their respective PRs are merged)

[ ] The Jira 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".