SOLR-16676: Http2SolrClient loss of MDC context - test fixes

[stillalex]

https://issues.apache.org/jira/browse/SOLR-16676

Description

I am changing the MDC copy to only happen on the final callback events, success or failure, that was the one that was important in my view. chasing the intermediary threads that are processing the request/response seems to not be a good idea and was causing the MDC to get lost on the way.

Ran beast 100 on this and the test passes.

[stillalex]

@risdenk please feel free to push #1443 on top of this with the changes you proposed

[risdenk]

@stillalex change looks good. I merged main, merged #1443, and ran tidy.

[stillalex]

thanks a lot @risdenk!

if it helps I also ran a 500 over night and it passed

solr$ ./gradlew beast -p solr/core --tests TestHttpRequestId -Ptests.dups=500
BUILD SUCCESSFUL in 10h 17m 47s
524 actionable tasks: 511 executed, 13 up-to-date