feat: Define strongly typed function interface

[garethgeorge]

Introduces a new Typed signature to the functions framework which provides automatic request deserialization and response serialization.

[conventional-commit-lint-gcf[bot]]

🤖 I detect that the PR title and the commit message differ and there's only one commit. To use the PR title for the commit history, you can use Github's automerge feature with squashing, or use automerge label. Good luck human!

-- conventional-commit-lint bot https://conventionalcommits.org/