Apply rate limits in LLM service (#15997)

Release Notes:

- N/A

---------

Co-authored-by: Marshall <marshall@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/collab/migrations_llm/20240806213401_create_usages.sql

@@ -1,15 +1,19 @@
+create table usage_measures (
+    id serial primary key,
+    name text not null
+);
+
+create unique index uix_usage_measures_on_name on usage_measures (name);
+
 create table if not exists usages (
     id serial primary key,
     user_id integer not null,
     model_id integer not null references models (id) on delete cascade,
-    requests_this_minute integer not null default 0,
-    tokens_this_minute bigint not null default 0,
-    requests_this_day integer not null default 0,
-    tokens_this_day bigint not null default 0,
-    requests_this_month integer not null default 0,
-    tokens_this_month bigint not null default 0
+    measure_id integer not null references usage_measures (id) on delete cascade,
+    timestamp timestamp without time zone not null,
+    buckets bigint[] not null
 );
 
 create index ix_usages_on_user_id on usages (user_id);
 create index ix_usages_on_model_id on usages (model_id);
-create unique index uix_usages_on_user_id_model_id on usages (user_id, model_id);
+create unique index uix_usages_on_user_id_model_id_measure_id on usages (user_id, model_id, measure_id);