Added GitHub CODEOWNERS

[ml-evs]

This is to force a review from either @CasperWA or I on all PRs. It would be great to split the package up a bit so that other contributors have some ownership. We will hopefully discuss this in the meeting today.

In the meeting we decided to also add other owners for mongo and elastic specifically (I won't tag Markus or Shyam again to avoid spam).

[codecov]

Codecov Report

Merging #664 (2fa6575) into master (790ab7d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #664   +/-   ##
=======================================
  Coverage   93.45%   93.45%           
=======================================
  Files          61       61           
  Lines        3299     3299           
=======================================
  Hits         3083     3083           
  Misses        216      216           

Flag	Coverage Δ
project	93.45% <ø> (ø)
validator	66.11% <ø> (ø)

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