add release plan #5714

Job	Run time
Build extensions	1m 22s
Test	2m 8s
ember-try (ember-lts-3.16)	1m 5s
ember-try (ember-lts-3.20)	1m 16s
ember-try (ember-lts-3.24)	1m 25s
ember-try (ember-lts-3.28)	1m 27s
ember-try (ember-release)	1m 19s
ember-try (ember-beta)	1m 30s
ember-try (ember-canary)	1m 12s
ember-try (ember-default-no-prototype-extensions)	1m 5s
Publish Chrome extension	8s
Publish Firefox extension	27s
Publish npm package	7s
Publish bookmarklet	0s
	14m 31s

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