chore(3.15.0): Add the installation manifests for 3.15.0 version (#5027) #1284

Job	Run time
frontend-checks	1m 18s
get-envs	5s
backend-checks	19s
docker-build-and-push-graphql-server	9m 59s
docker-build-and-push-event-tracker	10m 24s
docker-build-and-push-subscriber	8m 34s
docker-build-and-push-authentication-server	5m 48s
docker-build-and-push-frontend (litmusportal-frontend)	2m 28s
docker-build-and-push-frontend (litmusportal-frontend-path-litmuschaos, /litmuschaos)	2m 37s
	41m 32s

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