Enable diagnostic reports via ENV var for gstg

What does this MR do?

⚠ First, we need to merge:

• 1. gitlab-org/gitlab!91283 (merged)
• 2. !1949 (merged)

Enables diagnostic reports for staging.
Please note that it would only initialize the reporting daemon, no reports would be created until report_jemalloc_stats feature flag is enabled.

FF rollout issue: gitlab-org/gitlab#367845 (closed)
More on the reports feature: gitlab-org/gitlab!91283 (merged)
SRE support issue: gitlab-com/gl-infra/delivery#2486 (closed)

Author Check-list

Please read the Contributing document and once you do, complete the following:

• Check if all of the following apply:
  • Assign to the correct reviewer per the contributing document
  • Apply the correct metadata per the contributing document
  • Link to related MRs for applying the changes on other environments
  • Link to related Chef changes
  • If necessary link to a Criticality 4 Change Request issue

Reviewer Check-list

• Check if all of the following apply:
  • Reviewed the diff jobs to confirm changes are as expected
  • No changes shown in the diffs not associated with this MR - This may require a rebase or further investigation

Applier Check-list

• Make sure there is no ongoing deployment for the affected envs before merging (see #announcements slack channel)