Add source to quotes

[Snugug]

Description

Quotes should be able to include a source, and an optional link, in addition to an author

Suggested solution

Add source, plain text, with optional URL (for link) in addition to author. Either author or source should be required, and both can be included.

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Check that there isn't already an issue that requests the same feature to avoid creating a duplicate.
• Make sure this is a ChromeOS.dev (the ChromeOS documentation and news site) issue and not a general ChromeOS issue. If you're looking to request a feature for ChromeOS, please report a ChromeOS problem or send feedback instead.
• Check that this is a concrete feature request. For Q&A, either ask in the Chromebook Help Community or join the #chromeos or #chromeos-forum channels in the Google Developer Community Discord.