Add a capability to trigger a quartz job on-demand via the actuator endpoint

[mranile-dev]

Currently, SB is having actuator endpoints to retrieve details of Quartz scheduled jobs and its triggers. This feature request is to extend the actuators capability to be able to do the following:

1. On-demand trigger of any Quartz job(s)
2. Ability to override or update the existing cron expression of the specific job(s)

[philwebb]

We think that 1) is possible, and hopefully not too hard to implement. 2) is pretty hard because Quartz supports multiple trigger types.

[nosan]

I've worked a little bit on this issue, especially the trigger job on demand part. I've prototyped some changes in my branch.

To trigger a job on demand, overall does not require a lot of changes and can be implemented, but it requires some changes in AbstractWebFluxEndpointHandlerMapping and AbstractWebMvcEndpointHandlerMapping since both of them do not support Map<String, Object> as an endpoint parameter. (Consider as a bug? By the way, Jersey works fine)

To support Map<String, Object> as an endpoint parameter the following should be changed
in both classes:

@RequestBody(required = false) Map<String, String> body should be changed to @RequestBody(required = false) Map<String, Object> body, otherwise the following exception will be thrown:

[org.springframework.http.converter.HttpMessageNotReadableException: 
JSON parse error: Cannot deserialize value of type `java.lang.String` from Object value (token `JsonToken.START_OBJECT`)]

Regarding the ability to override or update the existing trigger of the specific job. I am
not sure whether it is worth supporting this at all. For example, I checked the QuartzSchedulerMBean interface and it does not have such functionality for JMX, at least I haven't found it. Overall, it could be implemented, but it requires a quite significant piece of work.

[mranile-dev]

Let's implement capability #1 for now if it's doable. It will be a good feature for remotely triggering the job on-demand without waiting on the next scheduled trigger. Thanks @nosan Cheers!