PHRAS-4010 Add mysql8 as alternative datastore #795

Job	Run time
build phraseanet-fpm / build	28s
build phraseanet-worker / build	37s
build phraseanet-nginx / build	24s
build phraseanet-setup / build	39s
build phraseanet-db / build	39s
build phraseanet-elasticsearch / build	24s
unit test	10m 42s
	13m 53s

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