[Angular] XM Cloud Forms support

[illiakovalenko]

• This PR follows the Contribution Guide
• Changelog updated
• Upgrade guide entry added

Description / Motivation

• Introduced a new Form component:
  • The component is a wrapper around the built Sitecore Form that allows you to fetch and render the form from Sitecore Edge.
  • The component is a part of the @sitecore-jss/sitecore-jss-angular package.
  • Component is rendered only on the client side.
  • Handles the case when FormId is not provided, custom error message is displayed.
  • Handles the case when network error occurs during fetching the form from Sitecore Edge, custom error message is displayed.
• Introduced a new InjectionToken EDGE_CONFIG to provide the configuration for the Form component to be able to fetch the form from Sitecore Edge.
• Introduced a plugins technique for the component factory generation to add extensebility for add-ons.
• Introduced a new "getEdgeProxyFormsUrl" method to get the URL for fetching the form from Sitecore Edge.

Testing Details

• Unit Test Added
• Manual Test/Other (Please elaborate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

[yavorsk]

Great work.
Please see only one comment.