* Introduce GeneratorSettings + cleanup
GeneratorSettings is an immutable settings object, intended to limit the
manipulation of generator settings.
To move to GeneratorSettings, lots of modification was done to
CodegenConfigurator. The goal here is that CodegenConfigurator
would create the contextual information required to initiate a
generator run:
* GeneratorSettings
* Workflow related settings
* Configuring "system" GeneratorProperties (ThreadLocal properties)
* Deserializing from file to config object
* Input spec document (OpenAPI, intending to target others)
ClientOpts was generally unused, and the few places it was being used
have been updated to pass the properties to
codegen.additionalProperties.
* Add sanity to system properties
The -D argument for the generate command is an application argument
which is easily confused for Java System Properties. This isn't the
case, as setting values here doesn't update the configuration in
System.getProperties().
This adds a warning and deprecation to that option, as defining these
values as system properties will also continue to work as expected. This
makes the -D application argument redundant and confusing.
* Contextualize generator/workflow settings
This splits settings relevant to generator configuration (the what) and
workflow configuration (the how) in an attempt to make configuration
easier to conceptualize.
* Update Gradle task w/ CodegenConfigurator setters
* Remove -D usage in scripts
* Add -p option for additional properties
* Regnerate samples
