feat(preview-service): allow metrics port to be configured

[iainsproat]

Description & motivation

If debugging or developing the Preview Service it is helpful to be able to assign a different port for the metrics server. This PR allows the port to be configured via the Helm Chart.

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