Add Codecov integration #849

Job	Run time
Smoke (latest, Phpunit)	24s
Unit (7.4, Phpunit)	1m 30s
Smoke (latest, CodingStyle)	19s
Unit (7.4, Phpunit Lowest)	1m 34s
Smoke (latest, StaticAnalysis)	15s
Unit (8.0, Phpunit)	1m 38s
Unit (8.0, Phpunit Lowest)	1m 35s
Unit (8.1, Phpunit)	1m 41s
Unit (8.1, Phpunit Lowest)	1m 32s
Unit (8.2, Phpunit)	1m 43s
Unit (8.2, Phpunit Lowest)	1m 43s
Unit (8.3, Phpunit)	1m 38s
Unit (8.3, Phpunit Lowest)	1m 36s
Unit (8.4, Phpunit)	1m 41s
Unit (8.4, Phpunit Lowest)	1m 37s
Unit (latest, Phpunit Burn)	8m 53s
	29m 19s

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