Build

use configurable keys for keeping static connections #159

Job	Run time
php-stan	24s
CS-Fixer	20s
Test (7.4, --prefer-lowest, test_phpunit_legacy)	1m 6s
Test (7.4, 5.4.*, test_phpunit_legacy)	1m 25s
Test (8, test_phpunit_legacy)	56s
Test (8.1, test)	1m 36s
Test (8.2, 6.3.*, test)	1m 4s
Test (8.3, 6.4.*, test)	1m 0s
Test (8.2, 7.0.*, test)	1m 2s
Test (8.3, dev, test)	1m 27s
Test (8.4, dev, test)	1m 30s
	11m 50s

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