Add a button to Sunshine's WebUI to switch the captured monitor

[NIICKTCHUNS]

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Feature Request

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Hello,

I've changed my Sunshine config to use the KWin capture method, I wanted to know / request this feature to add a button to change the display being hosted. XDG and KWin actually need this since the portals can ask the monitor or window to be captured

I've struggled a little trying to find what was the correct ID to put at the Display ID to change it, it would be much simpler with a button to change it

[ReenigneArcher]

LizardByte/roadmap#23