Fix inconsitent return type for the delete jobcluster

[hellolittlej]

Context

• current delete endpoint will return plain string when user is absent and json when error raises.
• we should keep the endpoint behavior consistent to always return application/json

Explain context and other details for this pull request.

Checklist

• ./gradlew build compiles code correctly
• Added new tests where applicable
• ./gradlew test passes all tests
• Extended README or added javadocs where applicable
  @Andyz26

[github-actions]

Test Results

661 tests  ±0   650 ✅ ±0   9m 7s ⏱️ +3s
152 suites ±0    11 💤 ±0 
152 files   ±0     0 ❌ ±0 

Results for commit e618254. ± Comparison against base commit 4ef1ba1.

♻️ This comment has been updated with latest results.