GPRD: Set GOGC for zoekt-indexer

What does this MR do?

Over the last week we've been suffering from OOM events with the zoekt-indexer. Our main theory right now is that GC is being too slow to react.

For example,

source

This MR sets GOGC to 50 to match the value set for zoekt-webserver

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)