fix(CPU load): Fix CPU load showing 0% in Runtime -> Metrics -> System

[five-iron]

The problem I am seeing in a downstream project is while viewing the Runtime->Metrics tab, CPU load almost always shows 0.00%. What I think is going on after some digging is that Jolokia is returning 0 for SystemCpuLoad due to this problem here: https://medium.com/infobipdev/the-java-cpu-usage-observer-effect-18808b18323f

The hidden cause of this discrepancy is the rename of the metric in JDK 14 from SystemCpuLoad to CpuLoad. The old metric was not removed, only deprecated in the API. JmxCollector pulls and publishes all available metrics, effectively calculating the same CPU usage twice in a row. The value was corrupted by merely measuring it — twice.

In the back end, getSystemCpuLoad() actually just calls getCpuLoad(), resulting in two nearly subsequent calls to that getCpuLoad method when the whole OperatingSystem mbean is called, which the medium article warns about.

From looking at the actual jolokia response object, CpuLoad in actually does have a real value, so this proposed change would just use that instead if available.

Made both fields conditional in the ts class in order to:

1. Support servers running <JDK14, before CpuLoad was added
2. Protect against SystemCpuLoad possibly getting removed in a future version of Java

[hawtio-ci]

Test results

Run attempt: 2109
Detailed summary

NAME	TESTS	PASSED ✅	SKIPPED 💤	FAILED ❌	ERRORS 🚫	TIME 🕖
results-quarkus-node(18)-java(17)-firefox	67	64	3	0	0	319.644
results-quarkus-node(18)-java(21)-firefox	67	64	3	0	0	312.047
results-quarkus-node(20)-java(17)-firefox	67	64	3	0	0	311.136
results-quarkus-node(20)-java(21)-firefox	67	64	3	0	0	312.277
results-springboot-node(18)-java(17)-firefox	67	63	4	0	0	311.126
results-springboot-node(18)-java(21)-firefox	67	63	4	0	0	313.075
results-springboot-node(20)-java(17)-firefox	67	63	4	0	0	311.965
results-springboot-node(20)-java(21)-firefox	67	63	4	0	0	312.914

[github-actions]

Test Results

  8 files  ±0    8 suites  ±0   41m 44s ⏱️ +2s
 66 tests ±0   64 ✅ ±0   2 💤 ±0  0 ❌ ±0 
536 runs  ±0  508 ✅ ±0  28 💤 ±0  0 ❌ ±0 

Results for commit 9fcd4bb. ± Comparison against base commit 3a9f4d6.

♻️ This comment has been updated with latest results.