CI/CD Analytics: Deprecate and remove unnecessary metric

Problem to solve

For CI/CD Analytics we introduced metrics by tab, which makes the total metric unnecessary (because that's the sum of the metrics by tab).

Proposal

After the 3 new metrics have been introduced, and we are confident they are working as expected, we should deprecate and remove the existing page-level usage metric called p_analytics_pipelines_monthly:

• Replace usage in Sisense.
• Confirm with ~"group::product intelligence" that the metric is not being used in Sisense (see example).
• Announce deprecation? (is there a process for this?)
• Remove from codebase.

Note: This was extracted from #342926 (closed) as suggested by @blabuschagne.