[DEVCON-6849] First part of new flow of adhoc mode

[smonero]

Change summary:

• create server.go in server/neptune/admin, this has NewServer(...), Start(), shutdown(), buildTerraformWorker(), and Healthz()
• modify user_config.go and tests to accomodate adminMode
• modify server.go in cmd to have new admin flow
• also create admin.go in cmd which has a func called NewServer() which then calls admin.NewServer(...)

[samrabelachew]

Thanks for starting to look at this, I'm of the opinion that we approach these changes by just injecting what we need to the new server rather than the opposite approach of adding all functionality and removing pieces later on.

[samrabelachew]

nice start, took a first past let me know if you have questions