Ease group declaration through code or properties with actuators

[christophejan]

Ease group declaration through code or properties with actuators by making actuator customizers global.

That way, actuator may be used the same way they already are on Default OpenAPI description.

springdoc:
  show-actuator: true
  group-configs:
    - group: all
      paths-to-match: /**
    - group: person
      paths-to-match: /person/**
    - group: x-actuator
      paths-to-match: ${management.endpoints.web.base-path:/actuator}/**

@Bean
public GroupedOpenApi allGroupedOpenApi() {
	return GroupedOpenApi.builder()
		.group("all")
		.pathsToMatch("/**")
		.build();
	}
}
@Bean
public GroupedOpenApi personGroupedOpenApi() {
	return GroupedOpenApi.builder()
		.group("person")
		.pathsToMatch("/person/**")
		.build();
	}
}
@Bean
public GroupedOpenApi xActuatorGroupedOpenApi(WebEndpointProperties endpointProperties) {
	return GroupedOpenApi.builder()
		.group(Constants.ACTUATOR_DEFAULT_GROUP)
		.pathsToMatch(endpointProperties.getBasePath() + Constants.ALL_PATTERN)
		.build();
	}
}

The PR is composed by 2 commits that are more easy to review one by one :

1. Ease group declaration through code or properties with actuators (Global actuator customizers)
2. Switch from statefull to stateless actuator customizers (otherwise, operationId depends on the order in which groups are requested). Actuator operation ids should be unique across each OpenAPI definition not across all OpenAPI definitions. Statefull cutomizer beans seems odd.

[bnasslahsen]

Thank you @christophejan for your PR!