use tenant-based remotewrite exporter

[alexandreLamarre]

Use fork of prometheusremotewrite exporter that injects tenant resource labels into X-Scope-OrgID header for cortex remote write. The resource label that is used to inject headers is configurable :

exporters:
  prometheusremotewrite:
    #...
    opni:
      tenant_resource_label: "__tenant_id__"

Misc changes:

• systemd's 247.3-7+deb11u1 is no longer listed in apt. upgraded to 247.3-7+deb11u2
• prometheusremotewrite exporter fork uses main's batchprocessor exporter, which has a breaking change, so upgraded that version in our builder config to match.