Add earliest partition date stat to table stats collector

[chenselena]

Summary

This PR adds the earliest partition date on a table as a stat to the table stats collector.

For tables where the retention policy has been set on a string type column, the stat is retrieved based on the retention column name, since this stat will be used as a comparison point for Openhouse alerting to identify if older partitions should have been cleaned up through retention jobs.
For tables that are partitioned on timestamp, it searches for the partition column name that is Timestamp. Openhouse only allows a table to be partitioned on 1 timestamp type column so we can identify that as the column set for retention.

Changes

• Client-facing API Changes
• Internal API Changes
• Bug Fixes
• New Features
• Performance Improvements
• Code Style
• Refactoring
• Documentation
• Tests

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Testing Done

• Manually Tested on local docker setup. Please include commands ran, and their output.
• Added new tests for the changes made.
• Updated existing tests to reflect the changes made.
• No tests added or updated. Please explain why. If unsure, please feel free to ask for help.
• Some other form of testing like staging or soak time in production. Please explain.

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Added unit testing.

Additional Information

• Breaking Changes
• Deprecations
• Large PR broken into smaller PRs, and PR plan linked in the description.

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[rohitkum2506]

Overall LGTM. Added a couple of comments.