Simplify docs and remove Docker local setup (#4783)

Having 2 different dev setups caused confusion, let's remove the Docker
local setup and recommend people install yarn locally.

Also simplified some docs by merging pages together, the recommend
self-hosting option is now the docker-compose / to adapt the
docker-compose.

packages/twenty-docker/twenty-postgres/init.sql

@@ -0,0 +1,4 @@
+CREATE DATABASE "default";
+CREATE DATABASE "test";
+CREATE USER twenty PASSWORD 'twenty';
+ALTER ROLE twenty superuser;