feat: add Owner Forge infrastructure chart

[aidansunbury]

Summary

• add a source-installable, namespace-local Helm chart for Owner Forge PostgreSQL, Temporal, and Temporal UI
• persist both PostgreSQL instances on Coder gp3 volumes and target Coder ARM nodes
• document direct installation from ~/helm-charts

Validation

• helm lint charts/other/ownerforge-infra
• helm template forge-infra-test charts/other/ownerforge-infra
• installed from this checkout in a Coder workspace with helm upgrade --install --wait
• verified both PVCs bound, Forge PostgreSQL authentication, Temporal schema setup, temporal ... cluster health = SERVING, and Temporal UI HTTP reachability
• uninstalled the validation release and confirmed no resources remained

[aidansunbury]

https://forge.owner.sh/tasks/tsk-VuGimTxC3DEz
Attempting to play around with an owner forge chart

[thisisamurray]

This approach is solid for a helm chart. For the chart-of-chart patterns, it's right in the middle. We just need to better understand the full scope of Forge Infrastructure (all the components we'd eventually want represented here) and if temporal/postgres together like this are reusable components by other services (or to break them apart in atomic elements)

Once we know that, then how to sub out the directory structure in here will be straightforward and we can make a more permanent home for it.