Add version selection for builtin metrics libraries

[jmacd]

Description:
Introduce a configuration mechanism to select which builtin instrumentation is used.

Link to tracking Issue:
Fixes #270

Testing:
New test coverage.

Documentation:
New README section.

[codecov-commenter]

Codecov Report

Base: 92.82% // Head: 93.00% // Increases project coverage by +0.17% 🎉

Coverage data is based on head (43f549e) compared to base (5b26476).
Patch coverage: 94.87% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #274      +/-   ##
==========================================
+ Coverage   92.82%   93.00%   +0.17%     
==========================================
  Files          71       71              
  Lines        3863     3890      +27     
==========================================
+ Hits         3586     3618      +32     
+ Misses        207      203       -4     
+ Partials       70       69       -1     

Impacted Files	Coverage Δ
pipelines/common.go	100.00% <ø> (ø)
pipelines/metrics.go	72.25% <92.59%> (+6.34%)	⬆️
launcher/config.go	89.39% <100.00%> (+1.76%)	⬆️

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