Provide option to create asyncapi lazy

[tvahrst]

The asyncapi and channel retrieval logic is impelemented in @PostConstruct methods inside DefaultAsyncApiService and DefaultChannelService - which means that the asyncapi detection runs during creation of the central spring(boot) context. This has an impact on the startup time of a spring boot application (especially if the scanning scope - springwolf.docket.base-package is large).

I suggest to provide an option to create the asyncapi lazy on first invocation of getAsyncApi. This option could be implemented as 'fail-fast' Property: true = current behavior, false = lazy asyncapi creation.

Motivation
Beside a better startup-performance, there is an additional advantage: we could pass context parameters between DefaultAsyncApiService and DefaultChannelService. This could help to implement additional functionality - for example an early validation of channel annotations against properties provided in a docket. (see additional feature request #293 ).

Technical details

• DefaultChannelService becames a stateless service which provides a channel map. @PostConstruct will be removed, the findChannels method will scan for channels and return the resulting map.
• DefaultAsyncApiService will cache a created asyncapi. The class supports two modes:
  • 'fail-fast' = true : The detection/creation of asyncapi will run in 'afterPropertiesSet' (synonym to @PostConstruct) - on bean creation. An exception will interrupt the spring context creation (i.e. the application start). The springwolf behavior stays compatible.
  • fail-fast = false: The detection/creation of asyncapi will run on first invocation of getAsyncApi. An exception during asyncapi creation will be cached and thrown each time getAsyncApi is invoced.

[timonback]

Thank your for the report, the issue has been addressed in the new release.

Feel free to reopen this issue if there is still something missing.