Bulk API fails with 503 response status

[chandrams]

Describe the bug
Invoked Bulk API with thanos datasource containing usage metrics for 1000 containers, it fails with 503 error

Equivalent cURL command :  curl -X GET 'http://kruize-openshift-tuning.apps.kruize-scalelab.h0b5.p1.openshiftapps.com/bulk?job_id=a0eb262f-d152-47de-809f-7898a9cccc0f&verbose=true'
Verbose GET Response Status Code:  503
Response 1: {
  "error": "Expecting value: line 1 column 1 (char 0)"
}

Tested with 2C / 4 Gi for both Kruize & DB pods

How to reproduce it

• Get the bulk scale test from this PR - Included kruize local scalability test using bulk API #1396
• Connect to the OCP cluster
• Execute the below cmd
  ./bulk_scale_test.sh -i quay.io/kruize/autotune_operator:0.2 -w 1 -r /tmp/results

Expected behavior
Bulk API job should fail with an appropriate error message

Relevant logs
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Environment:

• Kubernetes Cluster - openshift

Additional context
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