Add codecov configuration

[sliverc]

Description of the Change

• Ensure that PR covers 100% of diff (codecov/patch check)
• Disable project coverage as it may be misleading. (See clean python 2 codes #976 as an example where codecov/project fails as overall coverage is lower but actually in this case it is lower because code got removed).
• Disable GitHub comments to avoid notifications

Once this is merged we can make codecov/patch a requirement so PR won't be mergeable if diff is not covered. In the rare cases where a code bit cannot be tested it should be marked as # pragma: no cover in the code to make it clear.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #1002 (71a609b) into master (c4337f1) will not change coverage.
The diff coverage is n/a.

❗ Current head 71a609b differs from pull request most recent head 0eb44af. Consider uploading reports for the commit 0eb44af to get more accurate results

@@           Coverage Diff           @@
##           master    #1002   +/-   ##
=======================================
  Coverage   96.84%   96.84%           
=======================================
  Files          65       65           
  Lines        3925     3925           
=======================================
  Hits         3801     3801           
  Misses        124      124           

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