Retire unavailable Maven archetype docs

[hauptmedia]

Summary

• retire the unavailable Maven archetype repository/catalog instructions instead of pointing users at dead Operaton archetype resources
• replace old Camunda Artifactory/catalog setup with guidance to create projects directly from the current Operaton dependencies
• replace the stale public Spring Boot self-link in the testing guide with the local Spring Boot integration page
• clarify Operaton Assert history with the correct Camunda 7.17.0 reference and current Operaton repository wording
• clarify that Operaton does not currently publish Operaton-owned scenario testing or process test coverage extension repositories, and link only to the historical upstream community projects as compatibility references

Verification

• gh repo view operaton/operaton-archetypes returns not found
• gh repo view operaton/operaton-bpm-assert-scenario returns not found
• gh repo view operaton/operaton-bpm-process-test-coverage returns not found
• gh repo view camunda-community-hub/camunda-platform-scenario --json nameWithOwner,isArchived,url,description confirms the historical scenario project exists and is not archived
• gh repo view camunda-community-hub/camunda-process-test-coverage --json nameWithOwner,isArchived,url,description confirms the historical process test coverage project exists and is archived
• curl -fsI -L --max-time 20 https://github.com/camunda-community-hub/camunda-platform-scenario returns HTTP 200
• curl -fsI -L --max-time 20 https://github.com/camunda-community-hub/camunda-process-test-coverage returns HTTP 200
• curl -fsI -L https://github.com/camunda/camunda-bpm-platform/tree/7.17.0/test-utils/assert returns HTTP 200
• curl -fsI -L https://github.com/camunda/camunda-bpm-platform/tree/7.16.0/test-utils/assert returns HTTP 404
• rg -n "operaton-archetypes|operaton-bpm-assert-scenario|operaton-bpm-process-test-coverage|Operaton\\.17\\.0|docs\\.operaton\\.org/docs/documentation/user-guide/spring-boot-integration|pathes|visualises|html files|well documented|heavily used" docs/documentation/user-guide/process-applications/maven-archetypes.md docs/documentation/user-guide/testing/index.md -S returns no matches
• rg -n "Camunda 7.17.0|Camunda Platform Scenario|Camunda Process Test Coverage|Operaton-owned" docs/documentation/user-guide/testing/index.md -S confirms the replacement wording
• git diff --check
• npm run typecheck
• npm run build succeeds; Docusaurus still reports the known pre-existing broken link/anchor warnings handled separately in Fix docs link checks and enforce quality gates #115

[kthoms]

This MR should not be merged.

• It is still referring to a JavaEE setup, which we do not support. This should be updated to JakartaEE before.
• A Maven Archetype and archetype projects will be available through the Operaton Starter

If you are fine, close this.