Allow html messages in keys ending with `.html`

[AdrianFahrbach]

Clear and concise description of the problem

Currently the only way to use HTML messages without warnings is to set warnHtmlInMessage to false. This removes the warning for all keys though.

Suggested solution

Keys ending with .html should be allowed to have HTML messages. That way the warning can be "disabled" only where it is needed. This also provides a hint to the developer when working with this key, that it contains HTML.

Alternative

No response

Additional context

No response

Validations

• Read the Contributing Guidelines
• Read the Documentation
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.