[FEATURE] Add `return_metadata_only` prop (or something similar) to gmail-find-email action

[dannyroosevelt]

We should add a boolean prop to let users and Connect devs only return metadata for emails they're searching for, and to avoid bloating LLMs with unnecessary context if they don't need the content of emails.

Metadata should include everything from the current return object except for the snippet and payload.

[dannyroosevelt]

Let's also limit the max_results default to 20 instead of 100.