[WP Individual JP Plugin] Enable FF and add release notes

[thomashorta]

Fixes #18198

To test:

1. Install the app and clear the app storage
2. Login with an account that has problem sites
3. Verify the overlay is shown on top of the Login Epilogue (site picker right after login)

Another way to confirm is by going to App Settings > Debug Settings and confirming the wp_individual_plugin_overlay is ON by default.

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

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.

[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	pr18199-0351365
	Commit	0351365
	Direct Download	jetpack-prototype-build-pr18199-0351365.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	pr18199-0351365
	Commit	0351365
	Direct Download	wordpress-prototype-build-pr18199-0351365.apk

Note: Google Login is not supported on these builds.

[RenanLukas]

LGTM