Migrate to metal-apiserver

[majst01]

Description

Next microservice which gets migrated to MEP-4

Depends on: metal-stack/api#8

Closes: #37

TODO:

• change deployment
• add a helper to create proper tokens which is suitable for this service (image.list and partition.list is only required)
• add to the endpoint which gets called from the metal-hammer a service which creates a token for this machine, even better would be to add the token to the kernel cmdline, which is limited to 4096 chars which should be enough. This would eliminate the requirement of the extra http endpoint which is actually used for the hammer -> pixiecore communication.
• maybe also add a regular token refresh call into this service as well