add release plan #5707

Job	Run time
Test	2m 8s
Build extensions	1m 31s
ember-try (ember-lts-3.16)	1m 7s
ember-try (ember-lts-3.20)	1m 25s
ember-try (ember-lts-3.24)	1m 34s
ember-try (ember-lts-3.28)	1m 26s
ember-try (ember-release)	1m 12s
ember-try (ember-beta)	1m 14s
ember-try (ember-canary)	1m 22s
ember-try (ember-default-no-prototype-extensions)	1m 21s
Publish Firefox extension	36s
Publish Chrome extension	6s
Publish bookmarklet	0s
Publish GitHub release	0s
Publish npm package	4s
	15m 6s

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