Dynamic enablePWAKitPrivateClient that is based on config

[htuzel]

Previously, if you were using Template Extensibility feature, it was unnecessary to create whole overrides/app/components/_app-config/index.jsx if you only want to use PWAKitPrivateClient.

Description

Previously, if you were using Template Extensibility feature, it was unnecessary to create whole overrides/app/components/_app-config/index.jsx if you only wanted to use PWAKitPrivateClient.
it is said that Projects generated from PWA Kit 3.5 and above will be configured to use an SLAS private client by default in the documentation, with this PR, if you are using Template Extensibility, you can configure everything via configuration

Types of Changes

• Other changes (non-breaking changes that does not fit any of the above)

Changes

Added a new parameter on default.js file to manage PWAKitPrivateClient feature and it passed to _app-config file

How to Test-Drive This PR

• Create a new PWA-Kit project
• Create a private SLAS client and add/configure it for your SFCC instance
• Enable enablePWAKitPrivateClient by changing default false value
• See if it works

Checklists

General

• Changes are covered by test cases

Accessibility Compliance

You must check off all items in one of the follow two lists:

• There are no changes to UI
• Changes were tested with a Screen Reader (iOS VoiceOver or Android Talkback) and had no issues
• Changes comply with WCAG 2.0 guidelines levels A and AA
• Changes to common UI patterns and interactions comply with WAI-ARIA best practices

Localization

• Don't need localization change