Unified feedback form for Privacy Pro (#922)

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Please review the release process for BrowserServicesKit
[here](https://app.asana.com/0/1200194497630846/1200837094583426).

**Required**:

Task/Issue URL:
https://app.asana.com/0/1205922231854923/1207701941801991/f
iOS PR: duckduckgo/iOS#3172
macOS PR: duckduckgo/macos-browser#3058
What kind of version bump will this require?: Major/Minor/Patch

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Tech Design URL:
CC:

**Description**:

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**Steps to test this PR**:
1.
1.

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**OS Testing**:

* [ ] iOS 14
* [ ] iOS 15
* [ ] iOS 16
* [ ] macOS 10.15
* [ ] macOS 11
* [ ] macOS 12

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

Sources/BrowserServicesKit/PrivacyConfig/Features/PrivacyFeature.swift

@@ -117,6 +117,7 @@ public enum PrivacyProSubfeature: String, Equatable, PrivacySubfeature {
     case allowPurchaseStripe
     case isLaunchedOverride
     case isLaunchedOverrideStripe
+    case useUnifiedFeedback
 }
 
 public enum sslCertificatesSubfeature: String, PrivacySubfeature {

Sources/BrowserServicesKit/Subscription/SubscriptionFeatureAvailability.swift

@@ -22,6 +22,7 @@ import Subscription
 public protocol SubscriptionFeatureAvailability {
     var isFeatureAvailable: Bool { get }
     var isSubscriptionPurchaseAllowed: Bool { get }
+    var usesUnifiedFeedbackForm: Bool { get }
 }
 
 public final class DefaultSubscriptionFeatureAvailability: SubscriptionFeatureAvailability {
@@ -52,6 +53,10 @@ public final class DefaultSubscriptionFeatureAvailability: SubscriptionFeatureAv
         return isPurchaseAllowed || isInternalUser
     }
 
+    public var usesUnifiedFeedbackForm: Bool {
+        privacyConfigurationManager.privacyConfig.isSubfeatureEnabled(PrivacyProSubfeature.useUnifiedFeedback)
+    }
+
 // MARK: - Conditions
 
     private var isInternalUser: Bool {

Sources/PixelKit/PixelKit+Parameters.swift

@@ -70,6 +70,14 @@ public extension PixelKit {
         public static let reason = "reason"
 
         public static let vpnCohort = "cohort"
+
+        // Unified Feedback Form
+        public static let pproIssueDescription = "description"
+        public static let pproIssueSource = "source"
+        public static let pproIssueReportType = "reportType"
+        public static let pproIssueCategory = "category"
+        public static let pproIssueSubcategory = "subcategory"
+        public static let pproIssueMetadata = "customMetadata"
     }
 
     enum Values {