fix(preview-service): listen externally on metrics port

[iainsproat]

Description & motivation

The preview service application should only listen on localhost, as it currently does. However, the metrics endpoint should be externally accessible (by Prometheus) so should listen on 0.0.0.0 by default. This should be configurable.

Changes:

To-do before merge:

Screenshots:

Validation of changes:

Checklist:

• My pull request follows the guidelines in the Contributing guide?
• My pull request does not duplicate any other open Pull Requests for the same update/change?
• My commits are related to the pull request and do not amend unrelated code or documentation.
• My code follows a similar style to existing code.
• I have added appropriate tests.
• I have updated or added relevant documentation.

References