Always refresh metrics endpoint reldata on update-status

[sed-i]

Issue

• 368: metrics endpoint is not updated to ingressed address after relating to traefik.

Solution

Add self._set_scrape_job_spec as an observer to update-status.

Fixes #368.

Drawbacks

The user would have to wait for the update-status hook interval to elapse.

Context

This is an alternative to #384.

Testing Instructions

Release Notes

Always refresh metrics endpoint reldata on update-status.

[sed-i]

384 is probably the better solution. Closing this one.