Support the creation of databases as a service

[aguerra]

Basically we should be able to do:

teresa resource create mysql --set foo1=bar1 --set foo2=bar2 ...

where the variables are optional customizations (disk size, mysql version, etc). We should avoid to hardcode resource templates and instead use a secure transport such as https to get them.

Tasks

• [ ] Create the templates and the transport infra (suggestion: use helm as a starting point)
• [ ] Create a client or adapt the current storage to get the resources templates
• [ ] Create the resource command. Requirements:
  • create an arbitrary number of component resources in a specific order
  • sane template defaults with support for overriding values
  • interactive with user friendly messages
  • rollback all creations on any failure