Showcase SCSt 3.0 + Micrometer + RSocket Proxy for Prometheus monitoring

[sabbyanandan]

As we moved away from the older service-discovery to the new RSocket proxy architecture, it'd be useful to highlight the specific dependencies with the help of custom SCSt (3.0) applications.

Acceptance:

• Rename spring-cloud-dataflow-samples/tree/master/micrometer to spring-cloud-dataflow-samples/tree/master/micrometer-samples
• Rename spring-cloud-dataflow-samples/tree/master/micrometer/tasks to spring-cloud-dataflow-samples/tree/master/micrometer-samples/task-apps
• Describe or cross-link the description of the new architecture in the root README
• Highlight the required Micrometer Commons (from app starters BOM) + RSocket Proxy dependencies
• Add the apps under spring-cloud-dataflow-samples/tree/master/micrometer/stream-apps
• Update ref. docs, samples, and the microsite references to the old links