Content Preview setting: additional steps needed

[VakulinDev]

Priority: 1

A few steps must be added to automatically set up Content Preview feature

1. leadcms.core: in .env.sample add APISETTINGS__DEFAULTLANGUAGE="en" so it can be placed at the .env file automatically
2. leadcms.ai.next: in .env file, when setting NEXT_PUBLIC_LEADCMS_URL, value must be like: http://host.docker.internal:8080
   Where "internal:8080" is a LeadCMS url
3. LeadCMS Swagger: set values for LivePreviewUrlTemplate and PreviewUrlTemplate (http://localhost:8080/swagger/index.html where http://localhost:8080 is a default LeadCMS URL) in section PUT: /api/settings/system/{key}
   Use following format:

PreviewUrlTemplate
http://localhost:3000/{lang+slug}/

LivePreviewUrlTemplate
http://localhost:3000/{lang+slug}-{userId}/

where http://localhost:3000/ is the URL for leadcms.ai.next site using for a preview