Fix/operator process metrics

[jmthomas]

What changed

- Add OpenC3::ProcessStats to sample cpu/memory for an arbitrary pid,
  using Etc.sysconf rather than shelling out to getconf and splitting
  /proc/<pid>/stat from the last paren so a comm containing spaces or
  parens can't shift the field offsets
- Sample every child pid from Operator#publish_process_metrics each
  cycle, keeping one ProcessStats per microservice so cpu deltas
  accumulate across cycles and resetting it when a respawn changes pid
- Store operator reported values under MetricModel::PROCESS_PRIMARY_KEY
  and merge them on read, so the operator and the microservice are
  never two writers of one field
- Skip Metric.add_update_generator when OPENC3_OPERATOR_PROCESS_METRICS
  is set, which microservice_operator.rb sets on every child it spawns
- Drop the bootstrap metrics row in PluginMicroservice#run before exec
  so the stale sample is never published

Why it changed

plugin_microservice.rb exec()s the configured cmd, which replaces the
process image and kills the Metric update thread it just started. A cmd
that is itself an OpenC3::Microservice builds a new Metric and keeps
reporting, but a plugin running a Rails app, a python script or any
other binary never loads the OpenC3 libraries, so its cpu and memory
froze at whatever the bootstrap sampled and never changed again.

Testing strategy

Built enterprise and installed the CFDP plugin. Watched the System Health Microservice Metrics on the CFDP processes to verify the Sample Cpu Utilization was changing during scripts. Here is a screenshot of them at rest:

Here's an example of running the cfdp_test_suite.py. Note the Sample Cpu Utilization ... previously that would have just been 0 for the DEFAULT__USER__CFDP and DEFAULT__USER__CFDP2.

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[codecov]

Codecov Report

❌ Patch coverage is 93.93939% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.16%. Comparing base (2ad8e7b) to head (29a9071).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
openc3/lib/openc3/utilities/process_stats.rb	92.95%	5 Missing ⚠️
openc3/lib/openc3/operators/operator.rb	92.30%	2 Missing ⚠️
...c3/lib/openc3/microservices/plugin_microservice.rb	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3959      +/-   ##
==========================================
+ Coverage   80.11%   80.16%   +0.05%     
==========================================
  Files         901      903       +2     
  Lines       68370    68516     +146     
  Branches     2699     2699              
==========================================
+ Hits        54773    54929     +156     
+ Misses      12929    12918      -11     
- Partials      668      669       +1     

Flag	Coverage Δ
frontend	67.01% <ø> (-0.02%)	⬇️
python	80.12% <ø> (-0.01%)	⬇️
ruby-api	82.67% <ø> (+0.44%)	⬆️
ruby-backend	85.70% <93.93%> (+0.04%)	⬆️

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[sonarqubecloud]

Quality Gate failed

Failed conditions
4.9% Duplication on New Code (required ≤ 3%)
Code smells with severity Critical found (required < Major)

See analysis details on SonarQube Cloud