[QN] add `isShort` field to video entity #5940

Job	Run time
MacOS Checks (18.x)	9m 3s
Ubuntu Checks (18.x)	5m 37s
Build joystream/node	38s
Runtime Upgrade from production runtime	30s
Tests (full)	58m 56s
Tests (setupNewChain)	13m 28s
Tests (setupNewChainMultiStorage)	13m 35s
Tests (bonding)	14m 43s
Tests (storageSync)	22m 45s
	2h 19m 15s

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