Introduce jdbc.datasource-proxy.with-parent-only configuration property

[quaff]

If set jdbc.datasource-proxy.with-parent-only to true, then JDBC instrumentation should be ignored without parent Observation, I think it will mitigate #17

I have a system that polls a database every second with a simple query, and I will like to exclude it from traces reported to the Jaeger.

see micrometer-metrics/micrometer#3843 (comment)

[quaff]

We could use ObservationPredicate if micrometer-metrics/micrometer#3867 get merged, I'm going to close this.

	@Bean
	ObservationPredicate noParentlessDatabaseObservations() {
		return (name, context) -> {
			if (context instanceof DataSourceBaseContext) {
				return context.getParentObservation() != null;
			}
			return true;
		};
	}