feat: add URL helper text (resolves #311)

[greatislander]

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Description

This PR adds guidance for users indicating that URLs must include http:// or https://. Preferred to automatically adding http:// or https:// to user input as it's not possible to determine which scheme is correct (all sites support http but not all support https, and we should be directing people to https if possible—but if we automatically add https:// to URLs that may result in broken links).

Steps to test

1. Review the resource editor UI.

Expected behavior: Observe that instructions for all URL fields specify that the URL scheme must be provided.

Additional information

Not applicable.

Related issues

• Resolves Update URL field description text, or relax URL validation rules for resources #311.