feat(distro): add camunda spin & connect to all ditributions

related to #CAM-2303
feat(engine/spin): expose Spin in EL and Scripting

- allow users to use Spin's S(...) and XML(...) functions directly from
EL.

- make sure the Spin script environments are loaded by the process
engine.

- add simple ScriptEnvironment to provide evironment scripts in a
pluggable way.

related to #CAM-2303
feat(engine): add data input/output mapping

- support input/ouput parameters in camunda namespace.
- input/output is supported for tasks, events and subprocesses

related to #CAM-2288
feat(engine): add connector support

- add support for using connectors implementing the camunda-connect API

related to #CAM-2185