Enhance loading UI for product image in Blaze Campaign Creation form

- Update BlazeCampaignCreationForm.swift to add redacted and shimmering effects when loading product image
- Modify isLoadingProductImage visibility in BlazeCampaignCreationFormViewModel.swift to be read-only and set default to true

Author: pmusolino

WooCommerce/Classes/ViewRelated/Blaze/CampaignCreation/BlazeCampaignCreationForm.swift

@@ -274,6 +274,8 @@ private extension BlazeCampaignCreationForm {
                     .resizable()
                     .aspectRatio(contentMode: .fit)
                     .cornerRadius(Layout.cornerRadius)
+                    .redacted(reason: viewModel.isLoadingProductImage ? .placeholder : [])
+                    .shimmering(active: viewModel.isLoadingProductImage)
 
                 // Tagline
                 Text(viewModel.isLoadingAISuggestions ? "Placeholder tagline" : viewModel.tagline)

WooCommerce/Classes/ViewRelated/Blaze/CampaignCreation/BlazeCampaignCreationFormViewModel.swift

@@ -214,7 +214,7 @@ final class BlazeCampaignCreationFormViewModel: ObservableObject {
     @Published private(set) var error: BlazeCampaignCreationError?
     private var suggestions: [BlazeAISuggestion] = []
 
-    @Published private var isLoadingProductImage: Bool = false
+    @Published private(set) var isLoadingProductImage: Bool = true
 
     var canEditAd: Bool {
         !isLoadingAISuggestions