Add release target for workbench-session-init image #4925

Job	Run time
Fetch product daily/preview versions	6s
Connect - Daily	10m 43s
Connect Content Init - Daily	1m 7s
Base Image Previews	8m 47s
Package Manager - Daily	6m 39s
Package Manager - Preview	7m 14s
R Session Complete - Daily	11m 12s
R Session Complete - Preview	11m 22s
Workbench - Preview	12m 26s
Workbench - Daily	12m 16s
Workbench Session Init - Daily	3m 19s
	1h 25m 11s

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