Java agent cleanup

[grcevski]

This PR makes small improvements to the OBI java agent:

• I added a check to prevent the agent to be loaded (manually by using -javaagent:...) on non Linux systems. Since the ioctl API is Linux only, this will cause unexpected behaviour.
• I learned that you can pass data from a ByteBuddy method enter to exit with the @Advice.Enter annotation, so I changed to using that approach instead of the thread locals I was using.
• The thread pool instrumentations I added (the ForkJoin specifically) are used in the concurrent LRU implementation we are using (Caffeine), so I made sure we are not instrumenting those thread pools.

Checklist

• If this enhances / fixes / changes a core feature, I have updated the features documentation

[grcevski]

I caught two missing cleanup on return cases.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.27%. Comparing base (1024512) to head (ad3d043).
⚠️ Report is 1 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (1024512) and HEAD (ad3d043). Click for more details.

HEAD has 10 uploads less than BASE

Flag	BASE (1024512)	HEAD (ad3d043)
integration-test-vm-${ARCH}-${KERNEL_VERSION}	10	0

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1073      +/-   ##
==========================================
- Coverage   56.97%   47.27%   -9.70%     
==========================================
  Files         260      261       +1     
  Lines       22786    27455    +4669     
==========================================
- Hits        12982    12980       -2     
- Misses       8938    13608    +4670     
- Partials      866      867       +1     

Flag	Coverage Δ
integration-test	22.81% <ø> (-0.01%)	⬇️
integration-test-arm	0.00% <ø> (?)
integration-test-vm-${ARCH}-${KERNEL_VERSION}	?
k8s-integration-test	2.64% <ø> (ø)
oats-test	0.00% <ø> (ø)
unittests	48.53% <ø> (ø)

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[skl]

lgtm