chore: Add .github/CODEOWNERS file

[mwbrooks]

Summary

This pull request adds a .github/CODEOWNERS file to adhere to the Salesforce Open Source project requirements.

I've also added the Education team for the docs/ directory (even though no directory exists) and comments to match https://github.com/slackapi/python-slack-sdk.

Notes

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Requirements (place an x in each [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[mwbrooks]

@misscoded Thanks a lot for the approval! 🥇