feat: display list remote name on settings page

[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:

Displays the List's remote name on the settings page and expose it in the API. This makes sure the user will always see the name that is set on the remote ESP in their list.

How to test the changes in this Pull Request:

1. Configure Newsletters with an ESP with several lists
2. Visit Newsletters > Settings and make sure you see al the lists there
3. Make sure you have at least two lists that comes from the ESP (for example 2 mailchimp groups)
4. On Newsletters > Settings, customize the title of one of those lists
5. Go to the ESP dashboard and rename one of the lists
6. Back to the site, make sure you see the updated name in the Settings page
7. Confirm that the customizable title was updated only in the list that was not edited before. The list for which you had set up a custom title remained with the old title
8. Checkout feat: display list remote name on newsletter wizard newspack-plugin#3478 and go to Newspack > Engagement > Newsletters
9. Confirm the same behavior there

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

Attention: Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.

Project coverage is 20.16%. Comparing base (bcf221f) to head (8d0a772).
Report is 8 commits behind head on trunk.

Files with missing lines	Patch %	Lines
includes/class-newspack-newsletters-settings.php	0.00%	1 Missing ⚠️
includes/class-subscription-list.php	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk    #1672      +/-   ##
============================================
- Coverage     20.74%   20.16%   -0.59%     
- Complexity     2410     2413       +3     
============================================
  Files            46       46              
  Lines          9075     9895     +820     
============================================
+ Hits           1883     1995     +112     
- Misses         7192     7900     +708     

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