docker: Add image capable of loading policies/clients/jwks from an init.d directory

[aeneasr]

Currently, hydra is able to detect if an installation is new or not by checking if a client exists in the database already. If so, the following tasks are executed:

1. A new root client is generated with random credentials (can be changed with an environment variable)
2. A policy for said client is generated. It allows the client to do anything in hydra (thus "root" client)

We should update this part and add a couple of things:

1. We should rename the method doing this to "initializeNewInstallation" and move it to installation_helper.go
2. If a new installation is detected, root client and policy are generated as before
3. We look in <project-root>/init.d/policies for policies (json formatted) and in ``/init.d/clients`

[aeneasr]

Actually, it would be much better to have a docker image which is capable of doing that using the hydra CLI!

[pnicolcev-tulipretail]

Throwing together a dockerized go app to use the SDK to bootstrap initial clients was really easy, but this would be super convenient.

[aeneasr]

Examples how to do that are now at https://github.com/ory/examples