SpringBoot Add auto-configuration for Prometheus Exemplars

This PR adds Exemplars support for Micrometer Tracing. Please notice that this PR depends on https://github.com/spring-projects/spring-boot/pull/32399 because it needs all of those issues fixed first so the only real change in this PR is adding ExemplarsAutoConfiguration and ExemplarsAutoConfigurationTests.

Comment From: wilkinsona

Thank you, @jonatan-ivanov.