evalengine: Implement `PERIOD_DIFF` #473

Job	Run time
Set push variable	1s
Build and push vttestserver (mysql80)	1m 49s
Build and push lite (latest)	2m 20s
Build and push lite (percona80)	2m 11s
Build and push (bullseye, vtadmin)	1m 16s
Build and push (bullseye, vtorc)	32s
Build and push (bullseye, vtgate)	30s
Build and push (bullseye, vttablet)	41s
Build and push (bullseye, mysqlctld)	45s
Build and push (bullseye, mysqlctl)	37s
Build and push (bullseye, vtctl)	43s
Build and push (bullseye, vtctlclient)	39s
Build and push (bullseye, vtctld)	1m 17s
Build and push (bullseye, vtctldclient)	38s
Build and push (bullseye, logrotate)	19s
Build and push (bullseye, logtail)	32s
Build and push (bullseye, vtbackup)	41s
Build and push (bullseye, vtexplain)	37s
Build and push (bookworm, vtadmin)	1m 3s
Build and push (bookworm, vtorc)	54s
Build and push (bookworm, vtgate)	39s
Build and push (bookworm, vttablet)	38s
Build and push (bookworm, mysqlctld)	26s
Build and push (bookworm, mysqlctl)	38s
Build and push (bookworm, vtctl)	26s
Build and push (bookworm, vtctlclient)	30s
Build and push (bookworm, vtctld)	1m 9s
Build and push (bookworm, vtctldclient)	42s
Build and push (bookworm, logrotate)	37s
Build and push (bookworm, logtail)	39s
Build and push (bookworm, vtbackup)	42s
Build and push (bookworm, vtexplain)	38s
	25m 49s

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