feat: add screen cast with pipewire example

[SyedAhkam]

fixes: #155

[bilelmoussaoui]

I asked someone with pipewire knowledge if they can review it. If I don't hear anything by the weekend, will merge.

Would you mind adding a comment in the docs of both the camera/screencast portal pointing to this example?

[bilelmoussaoui]

And ignore the datas typo in https://github.com/bilelmoussaoui/ashpd/blob/master/.typos.toml

[SyedAhkam]

All done, lets wait for your friend now.

[SyedAhkam]

not sure why are tests failing even though I used ```rust,no_run

gotta use ignore

[rmader]

Had a look over the PW parts - only one comment, the rest look sensible to me