TP: Renamed Django project tp_backend -> playground #208

Job	Run time
gradle-tests	50m 56s
console-python-tests (lib/console_link)	27s
python-e2e-tests	20m 36s
console-python-tests (cluster_tools)	1m 59s
python-lint	9s
console-python-tests (console_api)	33s
style-check	1m 18s
workflow-info	3s
link-checker	3s
node-tests (./deployment/cdk/opensearch-service-migration)	46s
node-tests (./deployment/migration-assistant-solution)	24s
all-ci-checks-pass	1s
	1h 17m 15s

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