Update Mimir periodic query metric labels
The change modifies the query to retrieve the target for the GitLab service level agreement (SLA) from a specific tenant, "gitlab-gprd", instead of the global target. This change ensures that the SLA target is specific to the GitLab tenant in the "gitlab-gprd" environment, and that the data is correctly loaded into Snowflake.
Related issue: https://gitlab.com/gitlab-data/analytics/-/issues/20642