chore(content): Remove Swagger from Docs

Context
- Remove swagger references
- Adds explanatory content to migration guide about the removal

Co-authored-by: mboskamp
Co-authored-by: petros.savvidis

Related-to: camunda/camunda-bpm-platform#4467

Author: psavidis

content/installation/camunda-bpm-run.md

@@ -34,4 +34,3 @@ If you need to install Java Runtime Environment, you can [find the download from
 1. Start Camunda Run by executing the start script (start.bat for Windows, start.sh for Linux/Mac).
 1. Access the Camunda webapps (Cockpit, Tasklist, Admin) via http://localhost:8080/camunda/app/.
 1. Access the [REST API]({{< ref "/reference/rest/overview/_index.md" >}}) via http://localhost:8080/engine-rest (e.g. http://localhost:8080/engine-rest/engine).
-1. Access Swagger UI via http://localhost:8080/swaggerui/ to try out the REST API.