Add Newsletter Subscribers FF and update WPKit

[kean]

Code I used to test it (added to MySiteViewController.swift):

        Task {
            let service = PeopleServiceRemote(wordPressComRestApi: self.blog!.wordPressComRestApi!)
            do {
                let subs = try await service.getSubscribers(siteID: Int(self.blog!.dotComID!), page: nil, perPage: nil, parameters: .init())
                print(subs)
            } catch {
                print(error)
            }
        }

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 25.9. The due date for this milestone has already passed. Please assign it to a milestone with a later deadline or check whether the release for this milestone has already been finished.

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[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
	Configuration	Release-Alpha
	Build Number	27556
	Version	PR #24507
	Bundle ID	org.wordpress.alpha
	Commit	27b0c00
	Installation URL	1dih6n7hf5i2o

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[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
	Configuration	Release-Alpha
	Build Number	27556
	Version	PR #24507
	Bundle ID	com.jetpack.alpha
	Commit	27b0c00
	Installation URL	7caehf3r3ksv0

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[crazytonyli]

I have approvied the WPKit PR. This change can be discarded once the WPKit PR is merged.

[kean]

I updated it to point to wpios-edition.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud