Missing Schema file

I will work on it

Hi I added a basic schema file, this was the first time that I created a schema file please revise.

The bigger issue here is that each UsageType plugin should have its own config file.
It's not really worth fussing with a schema file under the current architecture.

The plugin settings should not be all lumped into one giant settings file.

Consider: if a 3rd party wants to extend usage_data.settings.yml, there's no way to ship the module with its own config, because the module needs to update a settings file from usage_data.

The schema file should include a schema like:

usage_data.usage_type.*:
    type: config_entity
    label: 'Usage Data Type'
    mapping:
      id:
        type: string
        label: 'UsageType Plugin ID'
      uuid:
        type: string
        label: 'UUID'
      enabled:
        type: boolean
        label: 'Enable or disable the plugin'
      use_queue:
        type: boolean
        label: 'Use queue to process items'
      dependencies:
        type: config_dependencies
        label: 'Dependencies'

Which would result in config files like the following, for example:
- usage_data.usage_type.generic.yml
- usage_data.usage_type.legacy.yml
- usage_data.usage_type.generic_counter.yml

The plugin manager would also need to be adjusted (significantly?) to handle these configs.

Opened new MR 25 with the proposed changes.

These will be breaking changes for anyone on an existing alpha.
Requires re-saving the Usage Data settings form.

@AaronBauman nice, I agree that each plugin should have it's own config; however, I do think we could change this to have an update hook to convert old config into new and not break existing installs. I'll take a stab at it if I can get some time next week.