RDoc-3312 Allow to define document id postfix in RavenDB ETL

[Danielle9897]

Issue links

• https://issues.hibernatingrhinos.com/issue/RDoc-3312/Allow-to-define-document-id-postfix-in-RavenDB-ETL
• https://issues.hibernatingrhinos.com/issue/RDoc-3794/RavenDB-ETL-Update-the-Studio-article

Additional description

Fixed articles:

• In ../server/ongoing-tasks/etl/basics.mdx:
  • Fix layout
  • Some text fixes (e.g. in syntax & loadTo method section)
• In ../server/ongoing-tasks/etl/raven.mdx:
  • Fix layout
  • Fix all sections under Panel "Transformation script options"
  • Added postfix info in section: "Setting a destination document ID postfix"
• In ../studio/database/tasks/ongoing-tasks/ravendb-etl-task:
  • Fix layout + text fixes
  • Updated images
  • Added sections about "Test area" & "Advanced options"

=> Notes:

1. This PR fixes only v7.2.
   Once approved, will apply the same modifications to earlier versions, since postfix was added in v5.4
2. In this PR, file raven.mdx was partially improved (the "Transformation script options" panel)
   Still need to:
   • Improve the other panels (especially "Deletions", which is Not written clearly).
   • Add "syntax" and a general example of creating the task from the Client API.
   • Do this in a dedicated/diff issue (or when handling "Reorganization"...)

---

Type of change

• Content - docs
• Content - cloud
• Content - guides
• Content - start pages/other
• New docs feature (consider updating /templates or readme)
• Bug fix
• Optimization
• Other

Changes in docs URLs

• No changes in docs URLs
• Articles are restructured, URLs will change, mapping is required (update /scripts/redirects.json file, set Documents Moved PR label)

Changes in UX/UI

• No changes in UX/UI
• Changes in UX/UI (include screenshots and description)