indexers: Fix autoscaling with authentication

It was missing the yaml relative to secret to to use with the proper authentication user. It was not an issue since it's currently deployed in staging without any authentication (and it's not deployed through the chart yet in production).

This also adds tests on the impacted part of the chart [1]

[1]

Tests

make test
docker run -ti --user 1000 --rm -v /home/tony/work/swh/sysadm-environment/swh-charts:/apps \
  "helmunittest/helm-unittest:3.11.1-0.3.0" swh

Chart [ swh ] swh
PASS  test graphql deployment  swh/tests/graphql_configmap_test.yaml
PASS  test graphql deployment  swh/tests/graphql_deployment_test.yaml
PASS  test graphql deployment  swh/tests/graphql_global_test.yaml
PASS  test graphql deployment  swh/tests/graphql_service_test.yaml
PASS  test indexers keda-secrets       swh/tests/indexers_keda_secrets_test.yaml
PASS  test loader_metadata configmap deployment        swh/tests/loader_metadata_configmap_test.yaml
PASS  test loader_metadata configmap utils deployment  swh/tests/loader_metadata_configmap_utils_test.yaml
PASS  test loader_metadata deployment  swh/tests/loader_metadata_deployment_test.yaml
PASS  test global loader metadata deployment   swh/tests/loader_metadata_global_test.yaml
PASS  test loader_metadata keda-scaling        swh/tests/loader_metadata_keda_autoscaling_test.yaml
PASS  test loader_metadata keda-secrets        swh/tests/loader_metadata_keda_secrets_test.yaml
PASS  test memcached deployment        swh/tests/memcached_deployment_test.yaml
PASS  test memcached deployment        swh/tests/memcached_global_test.yaml
PASS  test memcached service   swh/tests/memcached_service_test.yaml
PASS  test memcached ServiceMonitor    swh/tests/memcached_servicemonitor_test.yaml
Charts:      1 passed, 1 total
Test Suites: 15 passed, 15 total
Tests:       28 passed, 28 total
Snapshot:    0 passed, 0 total
Time:        110.160513ms

Refs. swh/infra/sysadm-environment#4794 (closed)

cc @teams/sysadmin