Add prompt before sending invalid commands

[cloudrac3r]

Description

This was previously a feature I added in #1435, but it got lost in a refactor. Here it is again.

When a message starts with / but didn't trigger a command, the popup will be shown. The popup allows sending it anyway, or going back to edit.

To make this work, I made the submit function async, which does not seem to have had any negative consequences.

This feature will prevent mistakes like this:

Type of change

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

[github-actions]

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