Feat/linter contacts methods

[leogermani]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

#1594 done again after its base epic branch got merged leaving it behind

In the effort of consolidating our data flows, we want to enforce that every contact update goes through the same route, starting at Newspack_Newsletters_Contacts class to make sure we have the propper logging.

However, we can't make all the internal methods private or protected.

This PHP Sniffer helps us avoid adding any new code that will bypass our intended flow. We'll need to add this sniffers to other Newspack plugins as well. - TBD how to do that

How to test the changes in this Pull Request:

1. checkout this branch
2. run ./vendor/bin/phpcs
3. Confirm you see some error in 2 files. (These errors are fixed in Add/logging #1574)
4. Does the message look good?
5. Try to add a method to one of the forbidden methods anywhere in the code.
6. Make sure the sniffer catches it

PS - the linting errors in the CI job are expected until we merge #1574

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 19.60%. Comparing base (dd56ab8) to head (550be52).
Report is 33 commits behind head on trunk.

Additional details and impacted files

@@            Coverage Diff            @@
##              trunk    #1611   +/-   ##
=========================================
  Coverage     19.60%   19.60%           
  Complexity     2370     2370           
=========================================
  Files            45       45           
  Lines          8922     8922           
=========================================
  Hits           1749     1749           
  Misses         7173     7173           

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[matticbot]

🎉 This PR is included in version 3.1.0-alpha.1 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀

[matticbot]

🎉 This PR is included in version 3.1.0 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀