OZG-3328 refactor xta adapter helm imagePullSecret

xta-adapter/src/main/helm/templates/_helpers.tpl

xta-adapter/src/main/helm/templates/image_pull_secret.yaml

xta-adapter/src/main/helm/templates/xta_adapter_cronjob.yaml

xta-adapter/src/test/helm-linter-values.yaml

xta-adapter/src/test/helm/image_pull_secret_test.yaml

xta-adapter/src/test/helm/xta_adapter_63_chars_test.yaml

...adapter/src/test/helm/xta_adapter_cronjob_basic_test.yaml

...pter/src/test/helm/xta_adapter_cronjob_bindings_test.yaml

.../src/test/helm/xta_adapter_cronjob_dummy_probes_test.yaml

xta-adapter/src/test/helm/xta_adapter_cronjob_env_test.yaml

...er/src/test/helm/xta_adapter_cronjob_image_pull_test.yaml

...ter/src/test/helm/xta_adapter_cronjob_resources_test.yaml

...c/test/helm/xta_adapter_cronjob_service_account_test.yaml

...apter/src/test/helm/xta_adapter_cronjob_volumes_test.yaml