Add CodeCov support

[pajlada]

Pull request checklist:

• CHANGELOG.md was updated, if applicable

Description

Generate and upload test coverage to codecov (on Ubuntu & latest version of go only)

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@6849e13). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #276   +/-   ##
=========================================
  Coverage          ?   28.97%           
=========================================
  Files             ?       43           
  Lines             ?     1101           
  Branches          ?        0           
=========================================
  Hits              ?      319           
  Misses            ?      744           
  Partials          ?       38           

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