[node-xmcloud-proxy] [Angular] /api/editing/config endpoint

[illiakovalenko]

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

Description / Motivation

• Introduced /api/editing/config endpoint
• Added CORS, Editing Secret handlers
• [sitecore-jss-proxy] Updates done to support extensibility to add new properties, modules. Made some restructuring:
  • express@^4.19.2 dependency is marked as a peer dependency, since we reference "express" related types, so it should match
  • Default scProxy middleware export is replaced by headlessProxy object that contains the middleware, ProxyConfig, ServerBundle properties
• [templates/angular] [templates/angular-xmcloud]:
  • Introduced server.exports.ts file to be able to have different variants per SXP / XMCloud addon's
  • generate-component-factory.ts now writes a list of components as well
  • metadata now can be generated at bootstrap stage
• Moved EDITING_ALLOWED_ORIGINS, QUERY_PARAM_EDITING_SECRET to sitecore-jss, since now these values are needed for xmcloud proxy middleware

Testing Details

• Unit Test Added
• Manual Test/Other Testing using "watch" script

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)

[art-alexeyenko]

Appears larger than I thought it would be.
Solid job, Illia, thank you. I left some comments, but I leave them to your discretion.