Revert "Merge branch 'gy-update-terraform-gcp-5.x' into 'main'"

What does this MR do?

MR reverts the recent Terraform GCP 5.x provider upgrade due to finding two new issues:

• google_compute_network data source now fails instantly when referring to a network that is also about to be created in 5.x
• google_service_networking_connection destroy calls appear to always fail in 5.x despite guidance

While the first can be worked around the second causes destroy calls to fail in Terraform incorrectly. Reverting for now to allow these issues to be addressed.

Related issues

Relates #762 (closed)

Author's checklist

When ready for review, the Author applies the workflowready for review label and mention @gl-quality/get-maintainers:

• Merge request:
  • Corresponding Issue raised and reviewed by the GET maintainers team.
  • Merge Request Title and Description are up-to-date, accurate, and descriptive
  • MR targeting the appropriate branch
  • MR has a green pipeline
  • MR has no new security alerts in the widget from the Secret Detection and IaC Scan (SAST) jobs.
• Code:
  • Check the area changed works as expected. Consider testing it in different environment sizes (1k,3k,10k,etc.).
  • Documentation created/updated in the same MR.
  • If this MR adds an optional configuration - check that all permutations continue to work.
  • For Terraform changes: set up a previous version environment, then run a terraform plan with your new changes and ensure nothing will be destroyed. If anything will be destroyed and this can't be avoided please add a comment to the current MR.
• Create any follow-up issue(s) to support the new feature across other supported cloud providers or advanced configurations. Create 1 issue for each provider/configuration. Contact the Quality Enablement team if unsure.