[REST API] Site Credentials login flow

[hichamboushaba]

For the REST API project, the authentication will use the site credentials before generating the Application Password that will be used for subsequent requests, and for this, we need to rework the site credentials screen to allow the following:

• Create a new site credentials screen, this screen will be specific to the WCAndroid app for now. [REST API] Introduce a new screen to handle site credentials login #8119
• Handle Authentication. [REST API] Introduce a new screen to handle site credentials login #8119
• Fetch Site info. [REST API] Introduce a new screen to handle site credentials login #8119
• Display an error if the site is not a WooCommerce site. [REST API] Check Woo installation #8125
• Display an error if application passwords are disabled. [REST API] Check Application Passwords status #8150
• Display an error if the user's role doesn't allow using the app. [REST API] Check user role #8156
• Unit tests. [REST API] unit tests for site credentials #8171

[peril-woocommerce]

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