Add project selection processing script

[AetherUnbound]

Description

Follow up to #3364, #3383, and #3412.

This PR adds the final processing step for project planning, which groups the project selection votes from the entire team.

See the README for more information on the script itself.

Testing Instructions

Due to the nature of the voting, this presently can only be tested by Openverse maintainers.

1. Run pipenv install in the new directory
2. Download the voting spreadsheet (access restricted) as a ".xlsx" file (default location is data/selection_votes.xlsx within the project_planning directory).
3. Run pipenv run python process_selection_votes.py and observe the output

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated 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.
• I ran the DAG documentation generator (if applicable).

Developer Certificate of Origin

Developer Certificate of Origin

Developer Certificate of Origin
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[dhruvkb]

LGTM, the bucket sizes also make sense.