perf: create idx cache table (#2140)

* perf: add idx cache

* Update crates/atuin-server-postgres/migrations/20240614104159_idx-cache.sql

* indentation

* remove trigger - for each row is too much, should be once per transaction

crates/atuin-server-postgres/migrations/20240614104159_idx-cache.sql

@@ -0,0 +1,8 @@
+create table store_idx_cache(
+  id bigserial primary key, 
+  user_id bigint,
+
+  host uuid,
+  tag text,
+  idx bigint
+);