collab: Allow enabling feature flags for all users (#16372)

This PR adds a new `enabled_for_all` column to the `feature_flags` table
to allow enabling a feature flag for all users.

Release Notes:

- N/A

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

@@ -8,6 +8,7 @@ pub struct Model {
     #[sea_orm(primary_key)]
     pub id: FlagId,
     pub flag: String,
+    pub enabled_for_all: bool,
 }
 
 #[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]