Goal:

• Aodh needs to be able to modify queries which come from alarms created by non-admin users.
• Aodh needs to do this on alarm creation. This makes the most sense. Modifying the queries during different times (i.e. during alarm evaluation) would need non-trivial modifications in Aodh and would result in less optimal performance.
• It's expected for users to create alarms on yet unknown metrics (i.e. when creating an autoscaling stack in a fresh cluster, it's expected the ceilometer_cpu metric isn't yet known to Prometheus when the alarms get created)
• This all means, the current PromQL parser in observabilityclient, which relies on querying Prometheus for list of currently known metric names to identify which parts of a PromQL query is a metric name isn't enough for Aodh.
• We need to update the PromQL parser, so that it's able to parse PromQL and do proper query modification (at the very least for ceilometer metrics) even when the metric names aren't yet known to prometheus.

Acceptance Criteria:

• The updated parser is implemented, merged and an observabilityclient version including that parser is released.