Add David and Matt as reviewers, and add actions for issue/PR assignment

[achals]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

none

[codecov-commenter]

Codecov Report

Merging #1942 (986d94c) into master (973f1c5) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1942   +/-   ##
=======================================
  Coverage   82.26%   82.26%           
=======================================
  Files          96       96           
  Lines        7669     7669           
=======================================
  Hits         6309     6309           
  Misses       1360     1360           

Flag	Coverage Δ
integrationtests	74.15% <ø> (ø)
unittests	59.39% <ø> (ø)

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[achals]

/verify-owners

[adchia]

/verify-owners

[adchia]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: achals, adchia

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[adchia]

/verify-owners