SpringBoot MDC trace and span IDs for Brave and OTel

Conditionals

• If Micrometer Tracing IS on the classpath
• For Brave
  • [MDC] If MDC is on the classpath
  • We will setup injecting spanId / traceId to MDC context
• For OTel:
  • [MDC] If MDC is on the classpath
  • We will setup injecting spanId / traceId to MDC context

superseeds https://github.com/spring-projects/spring-boot/pull/32214 split from https://github.com/spring-projects/spring-boot/pull/32480

Comment From: wilkinsona

I got confused by the separation of the 3 PRs and processed this all in #32480 in the end. Sorry.