chore: move crates into crates/ dir (#1958)

I'd like to tidy up the root a little, and it's nice to have all the
rust crates in one place

crates/atuin-server-postgres/migrations/20230315224203_create-deleted.sql

@@ -0,0 +1,5 @@
+-- Add migration script here
+alter table history add column if not exists deleted_at timestamp;
+
+-- queries will all be selecting the ids of history for a user, that has been deleted
+create index if not exists history_deleted_index on history(client_id, user_id, deleted_at);