docs: Use docker network instead of links in installation tutorial
Closes
* [Best Practices](access-control.md#best-practices)
* [The Warden](access-control.md#warden)
- [Install, Configure and Run ORY Hydra (15 minutes)](install.md#install-configure-and-run-ory-hydra)
+ - [Create a Network](install.md#create-a-network)
- [Start a PostgreSQL container](install.md#start-a-postgresql-container)
- [Install and run ORY Hydra](install.md#install-and-run-ory-hydra)
- [Install ORY Hydra without Docker](install.md#install-ory-hydra-without-docker)
