Fix for stability/metrics

[benjimin]

• Address Instability and ramping resource usage #337 (explosion of metrics) by labelling metrics by endpoint, rather than by path. Because the number of distinct paths is nearly unbounded (distinguishing those is a role for logs not metrics).
• Resolve repo staleness (previously passing tests now fail) by pinning a dependency version to the last compatible version (pending further updates).

[codecov]

Codecov Report

Merging #338 (bf8955b) into develop (fea217d) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           develop     #338   +/-   ##
========================================
  Coverage    86.22%   86.22%           
========================================
  Files           25       25           
  Lines         3077     3077           
========================================
  Hits          2653     2653           
  Misses         424      424           

Impacted Files	Coverage Δ
cubedash/_model.py	92.53% <100.00%> (ø)

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[jeremyh]

Thanks for looking into this

[jeremyh]

eodatasets regression is fixed in opendatacube/eo-datasets#220