Add Percentage True aggregation function

[Aritra8438]

Fixes #2944

This pull request adds support for Percentage true aggregation as a transformation step in the data explorer.

User will be able to:

• Get the percentage true of Boolean column based on Group By clause.

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Technical details

• Add Percentage_True(DBFunction) class to support percentage true aggregation
• Add percentage true suffix to the output alias of the aggregated column.
• Add Percentage True to the list of transformation steps in the data explorer.
• Add SQL for Boolean columns.
• Add test for the same.
  Screenshots

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the develop branch of the repository
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no
  visible errors.

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[Aritra8438]

Hi @mathemancer, @seancolsen. This PR is stacked on #2940

[mathemancer]

Nice work.