chore(mergify): add configuration file for automatic merge #462

Job	Run time
Test fixtures (test-ignore-tags)	4m 15s
Test fixtures (test-topo-order, --latest)	3m 22s
Test fixtures (test-date-order, --latest)	3m 27s
Test fixtures (test-topo-order-arg, --latest --topo-order)	4m 8s
Test fixtures (test-latest-with-one-tag, --latest)	4m 6s
Test fixtures (test-commit-footers)	3m 32s
Test fixtures (test-commit-preprocessors)	3m 16s
Test fixtures (test-custom-scope)	3m 26s
Test fixtures (test-limit-commits)	4m 9s
Test fixtures (test-skip-breaking-changes)	3m 53s
Test fixtures (test-split-commits)	4m 0s
Test fixtures (test-keep-a-changelog-links)	3m 31s
	45m 5s

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