[DISCO-3011] Migrate Load Test Images From Container Registry to Artifact Registry

[Trinaa]

References

JIRA: DISCO-3011

Description

The GCP container registry has been deprecated in favor of the artifact registry. This PR updated the load test scripts to use a new artifact registry when creating merino-locust images.

PR Review Checklist

Put an x in the boxes that apply

• [x] This PR conforms to the Contribution Guidelines
• [x] The PR title starts with the JIRA issue reference, format [DISCO-####], and has the same title (if applicable)
• [x] [load test: (abort|warn)] keywords are applied (if applicable)
• [x] Documentation has been updated (if applicable)
• [x] Functional and performance test coverage has been expanded and maintained (if applicable)