feat(artifactapi): cache stalwart webadmin zip (#157)

## Summary

- Adds \`stalwartlabs/webadmin/releases/latest/download/webadmin.zip\` to \`mutable_patterns\` in the \`github\` generic remote so the stalwart webadmin UI can be fetched through artifactapi rather than directly from GitHub.

## Notes

- Uses \`mutable_patterns\` (not \`immutable\`) because \`releases/latest\` resolves to whichever release is current and changes over time.
- Access URL: \`https://artifactapi.k8s.syd1.au.unkin.net/generic/github/stalwartlabs/webadmin/releases/latest/download/webadmin.zip\`

Reviewed-on: #157

apps/base/artifactapi/resources/conf.d/remote-generic.yaml

@@ -5,6 +5,7 @@ remotes:
     description: "GitHub releases and files"
     mutable_patterns:
       - ".*/archive/refs/heads/.*.tar.gz$"
+      - "stalwartlabs/webadmin/releases/latest/download/webadmin.zip$"
     immutable_patterns:
       - ".*/archive/refs/tags/.*.tar.gz$"
       - "ahmetb/kubectx/.*/kubectx_.*_linux_x86_64.tar.gz$"