Update grafana to v10 using Ark rpms

[sjpb]

Bumps grafana to v10 and uses Ark for stackhpc build, as upstream grafana repos appear to have removed 9.5.21 on or after 2025-04-25. As ark was in on-demand mode the packages are not there either.

Also makes it possible to change whether Packer cleans up resources from failed builds or not on a per-run basis.

Notes:

1. Ark is now in immediate mode for grafana, see Sync grafana repository content immediately stackhpc-release-train#399.
2. All Granfana dashboards are showing warnings for Angular depreciation, needs to be fixed before moving to v11.
3. The (forked) cloudalchemy.grafana role creates a repofile, and does so disabled to work around previous issues with grafana repos being unavaiable. In order to make minimal changes, this adds a custom repofile with the same content which is generated by the dnf_repos role.
4. Although a single repo is used for both RockyLinux 8 & 9, separate repo structures and snapshots have been added in case these need to diverge in future, and for consistency with other repo definitions.

[sjpb]

Fatimage build: https://github.com/stackhpc/ansible-slurm-appliance/actions/runs/14796564290

[sjpb]

Testing the above build manually failed, repo logic is wrong.

Fatimage build: https://github.com/stackhpc/ansible-slurm-appliance/actions/runs/14797550985

[sjpb]

image build: https://github.com/stackhpc/ansible-slurm-appliance/actions/runs/14856027334

[sjpb]

Tested all dashboards at this commit. All worked, all warned re. angular.

[wtripp180901]

If we're duplicating the repofile in the Grafana role, we'll need some way of protecting Ark creds

[sjpb]

Image build: https://github.com/stackhpc/ansible-slurm-appliance/actions/runs/14857401425

[wtripp180901]

LGTM

[edit added from Slack chat:] there is still one potential case where creds can get leaked, if you have dnf_repos_password defined but dnf_repos not in groups [then the check in bootstrap doesn't get run]. If you're using creds to do a local build from Ark directly, you could then run site without removing the creds, where dnf_repos wouldn't be in groups since iirc its just set to builder

[sjpb]

Image build: https://github.com/stackhpc/ansible-slurm-appliance/actions/runs/14859647057

[sjpb]

Image build https://github.com/stackhpc/ansible-slurm-appliance/actions/runs/14860103783

[wtripp180901]

LGTM