Add fixture for backend app #1387

Job	Run time
setup-matrix	8s
run-integration-tests (./examples/app-with-backend)	3m 21s
run-integration-tests (./examples/panel-datalinks)	2m 44s
run-integration-tests (./examples/datasource-basic)	4m 11s
run-integration-tests (./examples/app-with-rbac)	2m 24s
run-integration-tests (./examples/app-with-scenes)	1m 39s
run-integration-tests (./examples/datasource-streaming-websocket/streaming-websocket-plugin)	1m 31s
run-integration-tests (./examples/app-basic)	3m 19s
run-integration-tests (./examples/panel-frame-select)	2m 39s
run-integration-tests (./examples/datasource-streaming-backend-websocket/streaming-backend-websoc...	3m 20s
run-integration-tests (./examples/datasource-http)	2m 49s
run-integration-tests (./examples/datasource-http-backend)	2m 33s
run-integration-tests (./examples/app-with-extensions)	3m 29s
run-integration-tests (./examples/app-with-extension-point)	4m 31s
run-integration-tests (./examples/app-with-service-account)	2m 25s
run-integration-tests (./examples/app-with-dashboards)	2m 47s
run-integration-tests (./examples/panel-basic)	2m 46s
run-integration-tests (./examples/datasource-logs)	1m 34s
notify	0s
	48m 10s

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