feat(image-upload): allow for the option of showing a warning in upload display

[yellis]

Describe your changes

• Adds a warningMessage property to the image upload options
• When this property is set, will display the text in a s-notice s-notice__warning with the same setup as is used for the old editor
• Assumes that the text provided has been sanitized, per conventions used elsewhere

PR Checklist

• All new/changed functionality includes unit and (optionally) e2e tests as appropriate
• All new/changed functions have /** ... */ docs
• I've added the bug/enhancement and other labels as appropriate

Additional context

Addresses:

• MSO: Ask Wizard does not show the warning about images of code or errors
• MSO: Multiple issues when adding images in new Ask Wizard
• MSO: https://meta.stackoverflow.com/a/416327/51
• MSO: https://meta.stackoverflow.com/a/425093/51

It is setup for viewing in the Plugin Playground example page:

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[giamir]

@yellis I made some minore changes to stay consistent with the image upload options we already provide.
The option name is now warningNoticeHtml.
I am going to merge this soon and cut a release asap.
Thanks for your contribution.