feat(web): make google cast opt in (#18514)

* add setting switch

this isnt bound to anything yet

* make google casting opt-in

* doc updates

* lint docs

* remove unneeded translation items

* update mobile openai defs

* fix failing test

we need to mock user prefs since CastButton uses it

docs/docs/features/casting.md

@@ -2,6 +2,14 @@
 
 Immich supports the Google's Cast protocol so that photos and videos can be cast to devices such as a Chromecast and a Nest Hub. This feature is considered experimental and has several important limitations listed below. Currently, this feature is only supported by the web client, support on Android and iOS is planned for the future.
 
+## Enable Google Cast Support
+
+Google Cast support is disabled by default. The web UI uses Google-provided scripts and must retreive them from Google servers when the page loads. This is a privacy concern for some and is thus opt-in.
+
+You can enable Google Cast support through `Account Settings > Features > Cast > Google Cast`
+
+<img src={require('./img/gcast-enable.webp').default} width="70%" title='Enable Google Cast Support' />
+
 ## Limitations
 
 To use casting with Immich, there are a few prerequisites: