Better Java context propagation

[grcevski]

This PR introduces one fix and one improvement.

1. The code I had added for TC based L4 context propagation initially had some dead code which was invalid and we were mistakenly detecting spans with stale information.
2. Sometimes Java thread pools will connect on the parent thread to resolve the downstream service and then kick off a new thread pool thread to handle the outgoing connection. We can use this correlation to find the parent span, so I added extra code for matching based on the connection info.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.77%. Comparing base (0c09fd8) to head (a66f88d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1260      +/-   ##
==========================================
+ Coverage   78.11%   81.77%   +3.65%     
==========================================
  Files         135      135              
  Lines       11384    11384              
==========================================
+ Hits         8893     9309     +416     
+ Misses       1952     1546     -406     
+ Partials      539      529      -10     

Flag	Coverage Δ
integration-test	60.60% <ø> (+0.39%)	⬆️
k8s-integration-test	59.07% <ø> (?)
oats-test	36.42% <ø> (-0.05%)	⬇️
unittests	53.58% <ø> (-0.01%)	⬇️

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[rafaelroquetto]

LGTM!