Add SCSt 2.0 and Micrometer compatibility

[sabbyanandan]

As a developer, I'd like to upgrade to SCSt 2.0, so I can bring Micrometer compatibility.

Background:
Boot 1.x based Metric infrastructure is replaced with Micrometer in the 2.0 release. SCSt 2.0 builds on the new foundation already. The goal is to convert metrics-collector into another SCSt 2.0 consumer/sink.

Acceptance:

• Refactor and adapt to new infrastructure
• The collector functionally provides (via REST) the same data structure currently available in 1.x
• The newer Meter components and extra stats are "added" on top of it
• REST endpoints continue to operate against the same user credentials
• Unit/IT tests are refactored to adapt to the new infrastructure
• Migration guide provided (if necessary)

[tzolov]

This story depends on spring-projects/spring-boot#12594
Later enables the Spring Integration micrometer integration required to compute the stream rates.

[sabbyanandan]

We would also have to review the operational specifics of router-sink as part of this effort. Based on the findings and the complexity, we can split it into a different story.

[sabbyanandan]

Also, note, we do not have any specifical handling in Flo for router-sink, so that's something we need to take into account as well.