[JP Social] Create improvements feature config and enable it by default

[thomashorta]

Should be merged only after #18895

Sets the remote field jetpack_social_improvements_v1 to the JetpackSocialFeatureConfig and enables it by default.

To test:

1. Open the app
2. Go to Debug Settings
3. Verify the jetpack_social_improvements_v1 FeatureConfig is enabled by default
4. Go to Posts
5. Open a Draft post / create a new post
6. Open the Post Settings
7. Verify the JP Social section is available
8. Hit Publish
9. Verify the JP Social item is available in the pre-publish sheet

Regression Notes

1. Potential unintended areas of impact
   N/A

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)
   N/A, just feature flag work.

PR submission checklist:

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

[peril-wordpress-mobile]

	Fails
🚫	This PR is tagged with 'Do Not Merge' label.

Generated by 🚫 dangerJS

[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	pr18897-b8decc6
	Commit	b8decc6
	Direct Download	wordpress-prototype-build-pr18897-b8decc6.apk

Note: Google Login is not supported on these builds.

[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	pr18897-b8decc6
	Commit	b8decc6
	Direct Download	jetpack-prototype-build-pr18897-b8decc6.apk

Note: Google Login is not supported on these builds.

[RenanLukas]

Thanks for the PR, @thomashorta. It's working as expected.

LGTM