Block Types: Add `metadata` global attribute. #14034

Job	Run time
QUnit Tests	2m 15s
Slack Notifications / Prepare notifications	4s
Slack Notifications / Success notifications	4s
Slack Notifications / Cancelled notifications	0s
Slack Notifications / Fixed notifications	0s
Slack Notifications / Failure notifications	0s
Failed workflow tasks	0s
	2m 23s

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