Native support for CronJob: convert cron endpoints to fire once at startup

[nicolaferraro]

Related to apache/camel-k#1182

We should implement via a pluggable runtime module a customizer/loader that, when activated, makes sure an integration fires a single execution of every timer or quartz consumers at startup and immediately shutdown everything after the exchange is processed.

[lburgazzoli]

We should probably introduce a concept of source customizer/trait so we can apply multiple traits to ta source in a consistent way

[davsclaus]

Just mind if the user has both a timer/quartz route and a non cron like route in the same integration? I guess we need to check that this is the only route.

Also you can set camel main, the max number of messages to process (eg set it to 1 to have camel main terminate after that 1 message).

[lburgazzoli]

Yes we do something similar for the knative-source where we fail if there is more than one route. Unfortunately the camel-main do not yet support exit the application in camel-quarkus (we dependson quarkus command mode to be implemented for that but it is not yet ready)