Refactor strfry playbook for multiple instances

[dcadenas]

As per @mplorentz conversation:

Goals:

• All strfry instances deploy from the same branch.
• stryfry configuration is controlled through ansible inventory variables. We might need to do some tricks here when it comes to the plugins. If we have different plugins on different servers we might need to have a "plugin_set" variable with some arbitrary names that we branch on in the playbook tasks, enabling/disabling certain plugins based on the variable name. Maybe we ship the plugins as ansible template files or maybe they should just go in the docker image :man-shrugging::skin-tone-2: