Rename `stats_traffic_tab` config to `stats_traffic_subscribers_tab`

[irfano]

Part of https://github.com/wordpress-mobile/WordPress-Android/issues/20660

This adds stats_traffic_subscribers_tab and removes stats_traffic_tab flag by renaming the old flag. For now, the flag enables changes related to the old project, but these will be reviewed during the development of the new Subscribers project.

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To Test:

1. Log in.
2. Open "Me → Debug settings"
3. Verify that stats_traffic_subscribers_tab config is on the REMOTE FEATURES tab.

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Regression Notes

1. Potential unintended areas of impact

   • None

2. What I did to test those areas of impact (or what existing automated tests I relied on)

   • N/A

3. What automated tests I added (or what prevented me from doing so)

   • This change includes only renaming a flag. Not a case for automated tests.

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PR Submission Checklist:

• [x] I have completed the Regression Notes.
• [x] I have considered adding accessibility improvements for my changes.
• [x] I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

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Testing Checklist (strike-out the not-applying and unnecessary ones):

• [ ] ~WordPress.com sites and self-hosted Jetpack sites.~
• [ ] ~Portrait and landscape orientations.~
• [ ] ~Light and dark modes.~
• [ ] ~Fonts: Larger, smaller and bold text.~
• [ ] ~High contrast.~
• [ ] ~Talkback.~
• [ ] ~Languages with large words or with letters/accents not frequently used in English.~
• [ ] ~Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)~
• [ ] ~Large and small screen sizes. (Tablet and smaller phones)~
• [ ] ~Multi-tasking: Split screen and Pop-up view. (Android 10 or higher)~

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
3.5% Duplication on New Code

See analysis details on SonarCloud

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr20661-af9901f
	Commit	af9901f22885c181977364ceeb56e9402197b4ad
	Direct Download	jetpack-prototype-build-pr20661-af9901f.apk

Note: Google Login is not supported on these builds.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Flavor	Jalapeno
	Build Type	Debug
	Version	pr20661-af9901f
	Commit	af9901f22885c181977364ceeb56e9402197b4ad
	Direct Download	wordpress-prototype-build-pr20661-af9901f.apk

Note: Google Login is not supported on these builds.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 30.95238% with 29 lines in your changes are missing coverage. Please review.

Project coverage is 40.43%. Comparing base (1cd2d9a) to head (af9901f).

Files	Patch %	Lines
...ts/refresh/lists/widget/WidgetBlockListProvider.kt	0.00%	5 Missing :warning:
...rdpress/android/ui/stats/refresh/StatsViewModel.kt	40.00%	1 Missing and 2 partials :warning:
...esh/lists/widget/minified/MinifiedWidgetUpdater.kt	0.00%	3 Missing :warning:
...s/refresh/lists/widget/today/TodayWidgetUpdater.kt	0.00%	3 Missing :warning:
.../lists/widget/weeks/WeekViewsWidgetListProvider.kt	0.00%	3 Missing :warning:
...fresh/lists/widget/weeks/WeekViewsWidgetUpdater.kt	0.00%	3 Missing :warning:
...ists/widget/today/TodayWidgetBlockListViewModel.kt	50.00%	0 Missing and 2 partials :warning:
...resh/lists/widget/today/TodayWidgetListProvider.kt	0.00%	2 Missing :warning:
...resh/lists/widget/views/ViewsWidgetListProvider.kt	0.00%	2 Missing :warning:
...d/ui/stats/refresh/utils/SelectedSectionManager.kt	50.00%	1 Missing and 1 partial :warning:
... and 1 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## trunk #20661 +/- ## ========================================== - Coverage 40.43% 40.43% -0.01% ========================================== Files 1485 1485 Lines 68464 68468 +4 Branches 11323 11323 ========================================== + Hits 27686 27687 +1 - Misses 38266 38269 +3 Partials 2512 2512 ```

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