Update GAR & GHCR Image Tagging to MozCloud Spec

[data-sync-user]

Per MozCloud’s spec on Container Images and Continuous Deployment, we want to align our image tagging in GAR and GHCR to match the org-wide standard. This simplifies our Postgres and standard Spanner releases and includes the release date.

Tags must consist of:

• A short Git commit SHA (10 characters)
• A UTC timestamp in the format YYYYMMDDTHHMMSS

<short-sha>-<YYYYMMDDTHHMMSS>

Example:

• dd295fd679-20250513T194029

Document: https://mozilla-hub.atlassian.net/wiki/spaces/SRE/pages/1676935173/Standards+Container+Images#Future%3A-Continuous-Deployment

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