UI: Add option to warn on stop recording

OBS has an option to warn before stopping a stream, but it doesn't have
a similar warning for recording. This can result in a recording being
unintentionally stopped.

Add an option to warn when the "Stop Recording" button is pressed.

Note: While OBS also has an option to warn on stream start, this
patch purposefully does not add similar warn on recording start option.
This is because accidentally starting to record isn't risky in the same
way that accidentally starting to stream is.
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f