Add Labs screen for beta testing of public features (#5465)

* Add Labs screen:

- Make `Feature` have an `isInLabs` boolean to distinguish private feature flags from public ones.
- Have `FeatureFlagsService` provide the list of available flags.
- Display the labs item in the settings screen only if there are available public features.
- Remove public feature toggles from developer options.
- Implement the labs screen with the public features.
- Add a clear cache step to the threads feature toggle
- Update screenshots

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Co-authored-by: ElementBot <android@element.io>

libraries/featureflag/ui/src/main/kotlin/io/element/android/libraries/featureflag/ui/model/FeatureUiModel.kt

@@ -7,9 +7,12 @@
 
 package io.element.android.libraries.featureflag.ui.model
 
+import io.element.android.libraries.designsystem.theme.components.IconSource
+
 data class FeatureUiModel(
     val key: String,
     val title: String,
     val description: String?,
+    val icon: IconSource?,
     val isEnabled: Boolean
 )

libraries/featureflag/ui/src/main/kotlin/io/element/android/libraries/featureflag/ui/model/FeatureUiModelProvider.kt

@@ -12,7 +12,7 @@ import kotlinx.collections.immutable.persistentListOf
 
 fun aFeatureUiModelList(): ImmutableList<FeatureUiModel> {
     return persistentListOf(
-        FeatureUiModel("key1", "Display State Events", "Show state events in the timeline", true),
-        FeatureUiModel("key2", "Display Room Events", null, false),
+        FeatureUiModel(key = "key1", title = "Display State Events", description = "Show state events in the timeline", icon = null, isEnabled = true),
+        FeatureUiModel(key = "key2", title = "Display Room Events", description = null, icon = null, isEnabled = false),
     )
 }