Add codecov integration

[mbeacom]

Purpose

The goal of this PR is to add automated coverage reports via https://codecov.io/

Additional steps required

• Eventually needs repo owner to configure the integration at: https://github.com/integration/codecov
• Configure GitHub policy to allow or deny contributor ability to override the integration PR enforcement in the event of a decrease in coverage

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@bf8d15c). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #687   +/-   ##
=========================================
  Coverage          ?   66.16%           
=========================================
  Files             ?       16           
  Lines             ?     1407           
  Branches          ?      215           
=========================================
  Hits              ?      931           
  Misses            ?      429           
  Partials          ?       47

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