Remote feature flag for New Tab Page Improvements (#3294)

Task/Issue URL:
https://app.asana.com/0/72649045549333/1207539163549338/f
Tech Design URL:
CC:

**Description**:

Adds a flag allowing to remotely enable/disable New Tab Page
Improvements (sections) feature. Currently used as `.remoteDevelopment`,
will be updated to `.remoteReleasable` once the feature is complete.

**Steps to test this PR**:
1. Set Internal user flag
2. In Debug menu override Privacy Configuration json to
`http://www.jsonblob.com/api/1279014885881929728`
3. Reopen New Tab Page - feature should be visible now

**Definition of Done (Internal Only)**:

* [ ] Does this PR satisfy our [Definition of
Done](https://app.asana.com/0/1202500774821704/1207634633537039/f)?

---
###### Internal references:
[Software Engineering
Expectations](https://app.asana.com/0/59792373528535/199064865822552)
[Technical Design
Template](https://app.asana.com/0/59792373528535/184709971311943)

Author: dus7

Configuration/Version.xcconfig

@@ -1 +1 @@
-MARKETING_VERSION = 7.135.0
+MARKETING_VERSION = 7.136.0

Core/AppPrivacyConfigurationDataProvider.swift

@@ -23,8 +23,8 @@ import BrowserServicesKit
 final public class AppPrivacyConfigurationDataProvider: EmbeddedDataProvider {
 
     public struct Constants {
-        public static let embeddedDataETag = "\"3310d00f227a02b53a16ed4af90afee5\""
-        public static let embeddedDataSHA = "7371e7fd3293e42638aa3bd3905a205e70827b2fd980848af108c82cedabf8be"
+        public static let embeddedDataETag = "\"38047fbabac1af7f77112ee692d5d481\""
+        public static let embeddedDataSHA = "ee998861bbed8b784a7f19caafd76a8f6eb9a82160b0b6ddb21d97e67332b38f"
     }
 
     public var embeddedDataEtag: String {

Core/FeatureFlag.swift

@@ -74,7 +74,7 @@ extension FeatureFlag: FeatureFlagSourceProviding {
         case .history:
             return .remoteReleasable(.feature(.history))
         case .newTabPageSections:
-            return .internalOnly
+            return .remoteDevelopment(.feature(.newTabPageImprovements))
         case .duckPlayer:
             return .remoteReleasable(.feature(.duckPlayer))
         case .sslCertificatesBypass: