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/src/llm/db/tables/usage_measure.rs

@@ -0,0 +1,35 @@
+use crate::llm::db::UsageMeasureId;
+use sea_orm::entity::prelude::*;
+
+#[derive(
+    Copy, Clone, Debug, PartialEq, Eq, Hash, strum::EnumString, strum::Display, strum::EnumIter,
+)]
+#[strum(serialize_all = "snake_case")]
+pub enum UsageMeasure {
+    RequestsPerMinute,
+    TokensPerMinute,
+    TokensPerDay,
+    TokensPerMonth,
+}
+
+#[derive(Clone, Debug, PartialEq, DeriveEntityModel)]
+#[sea_orm(table_name = "usage_measures")]
+pub struct Model {
+    #[sea_orm(primary_key)]
+    pub id: UsageMeasureId,
+    pub name: String,
+}
+
+#[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]
+pub enum Relation {
+    #[sea_orm(has_many = "super::usage::Entity")]
+    Usages,
+}
+
+impl Related<super::usage::Entity> for Entity {
+    fn to() -> RelationDef {
+        Relation::Usages.def()
+    }
+}
+
+impl ActiveModelBehavior for ActiveModel {}