Disable password generation for burner windows (#3024)

Task/Issue URL: https://app.asana.com/0/1203822806345703/1207877600791247/f
Tech Design URL:
CC:

Description:
Disables password generation in fire windows, avoiding confusion since generated credentials are not currently autosaved in fire windows

DuckDuckGo/Tab/TabExtensions/AutofillTabExtension.swift

@@ -200,7 +200,7 @@ extension AutofillTabExtension: SecureVaultManagerDelegate {
         var supportedFeatures = ContentScopeFeatureToggles.supportedFeaturesOnMacOS(privacyConfigurationManager.privacyConfig)
 
         if !passwordManagerCoordinator.isEnabled,
-           AutofillNeverPromptWebsitesManager.shared.hasNeverPromptWebsitesFor(domain: domain) {
+           AutofillNeverPromptWebsitesManager.shared.hasNeverPromptWebsitesFor(domain: domain) || isBurner {
             supportedFeatures.passwordGeneration = false
         }