revert old change to backend MAU, fix frontend MAU

[kevinkarchacryl]

I'm reverting the backend changes I made in Nov from this PR https://github.com/datahub-project/datahub/pull/11918/files

With my changes to the frontend, the MAU chart ticks now have just the month:
After:

Before ticks would show (for Oct):

• The PR conforms to DataHub's Contributing Guideline (particularly Commit Message Format)
• Links to related issues (if applicable)
• Tests for the changes have been added/updated (if applicable)
• Docs related to the changes have been added/updated (if applicable). If a new feature has been added a Usage Guide has been added for the same.
• For any breaking change/potential downtime/deprecation/big changes an entry has been made in Updating DataHub

[codecov]

Codecov Report

Attention: Patch coverage is 5.88235% with 32 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../analyticsDashboard/components/TimeSeriesChart.tsx	5.88%	32 Missing ⚠️

Files with missing lines	Coverage Δ
.../analyticsDashboard/components/TimeSeriesChart.tsx	42.92% <5.88%> (-6.78%)	⬇️

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