Add check_is_channel_participant

Refactor permission checks to load ancestor permissions into memory
for all checks to make the different logics more explicit.

crates/collab/src/db/tables/channel.rs

@@ -7,7 +7,7 @@ pub struct Model {
     #[sea_orm(primary_key)]
     pub id: ChannelId,
     pub name: String,
-    pub visbility: ChannelVisibility,
+    pub visibility: ChannelVisibility,
 }
 
 impl ActiveModelBehavior for ActiveModel {}