Move incident metrics logic to shared location

Related to #340852 (closed)

This moves the metric image component & related files into a shared location, in preparation of frontend code for metric image uploading for Alerts.

Changes include:

• Make the Store & actions etc generic (use modelId), and normalise to issueId at the latest stage).
• Externalise the service from actions.js and allow service to be passed in via a factory.
• Rename MetricImage to MetricImageTable to better describe it.

To test

1. Install a Premium or higher license.
2. Navigate to the incident list (Monitor -> Incidents)
3. Create a new incident.
4. View the incident, navigate to the Metrics tab.