Asynchronous return execution ID upon playbook trigger API

[lucamrgs]

Problem: execution ID from trigger API call is returned only upon execution completed. This makes it not possible to query the Reporter by execution ID.

Solution: make trigger API call execution asynchronous and return execution ID

[lucamrgs]

Method:

• Two pull requests, one for async return exec id, one for solving race conditions on reporting via channel
• No returns of error anymore from the execution as they're handled within reporting
• Detach details object from decomposer property
• Listen to channel in trigger api (as in internal/fin/protocol/awaitresultortimeout)
• Safe race conditions via mutex

[lucamrgs]

I am using a public property for the trigger API channel in order to be able to test it