Add constants for private event #4116

Job	Run time
Basic Checks	2m 13s
Unit Tests	22m 20s
Integration Tests (raft)	13m 26s
Integration Tests (pvtdata)	11m 0s
Integration Tests (pvtdatapurge e2e)	20m 35s
Integration Tests (ledger)	13m 20s
Integration Tests (lifecycle)	5m 35s
Integration Tests (smartbft)	20m 57s
Integration Tests (discovery gossip devmode pluggable)	8m 31s
Integration Tests (gateway idemix pkcs11 configtx configtxlator)	16m 30s
Integration Tests (sbe nwo msp)	7m 53s
	2h 22m 20s

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