Bump gitlab-exporter to 10.3.0

What does this MR do?

This updates the gitlab-exporter service to the latest version 10.3.0, which in return updates Puma to the latest available version 5.3.2.

This MR supports the changes in gitlab-org/charts/gitlab!2030 (merged)

Related issues

General maintenance.

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes: See gitlab-org/charts/gitlab!2030 (merged)
• [-] Documentation created/updated
• [-] Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated: +58MB, but unlikely to be attributable to a Puma minor version bump (though not certain); !682 (comment 589968508)