[Docs Agent] Docs Agent release version 0.4.0

[kyolee415]

Description of the change

• Multi-modal support: The Docs Agent CLI supports image, audio, and video files as part of a prompt to the Gemini model.
• Formatted output: Select the format of Docs Agent CLI's responses with the --response_type json and --plaintext options.
• Autocomplete script: The autocomplete.sh script is added to include Docs Agent CLI commands and options, making it easier and faster to use the Docs Agent CLI on a terminal.

Motivation

Docs Agent's 0.4.0 release: Multi-modal support

Type of change

Choose one: (Feature request)

Checklist

• [ X] I have performed a self-review of my code.
• [ X] I have added detailed comments to my code where applicable.
• [ X] I have verified that my change does not break existing code.
• [ X] My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• [ X] I am familiar with the Google Style Guide for the language I have coded in.
• [ X] I have read through the Contributing Guide and signed the Contributor License Agreement.