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/20220421174016_larger-commands.sql

@@ -0,0 +1,3 @@
+-- Make it 4x larger. Most commands are less than this, but as it's base64
+-- SOME are more than 8192. Should be enough for now.
+ALTER TABLE history ALTER COLUMN data TYPE varchar(32768);