Adds a composer prompt on the home screen to invite users to post (#9464)

* Add a composer prompt on home

* Added image upload button

* Feed composer buttons

* Feed composer styles

* Add client events, auto-open gallery when button is pressed

* Add feature gate

* Move gate check to last

* Small style cleanups

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Co-authored-by: Eric Bailey <git@esb.lol>

src/lib/statsig/gates.ts

@@ -9,5 +9,6 @@ export type Gate =
   | 'onboarding_add_video_feed'
   | 'onboarding_suggested_starterpacks'
   | 'remove_show_latest_button'
+  | 'show_composer_prompt'
   | 'test_gate_1'
   | 'test_gate_2'