feat: add bigframes.bigquery.aead.* scalar functions

[tswast]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request introduces a new configuration file, aead.yaml, which defines several GoogleSQL scalar functions for AEAD encryption and decryption, including aead.decrypt_bytes, aead.decrypt_string, aead.encrypt, and their envelope counterparts. I have no feedback to provide.