Relates to coder/internal#22

Motivation

#14274 added detailed per-provisioner-job workspace build timings and inserted them into the database. These are exposed in the UI per workspace, but there is no top-level aggregated Prometheus metric for operators to monitor.

Proposed Solution

Expose provisioner job timings as a histogram aggregated by:

• template_name
• template_version
• job_type (template_version_import, template_version_dry_run, workspace_build)
• provisioner_type (terraform, echo)
• stage (init, plan, graph, apply)

NOTE: the above is a proposal only and not final.