Add support for signaling an external process via pid file #441

Job	Run time
build-images	59s
cache-deps (linux)	15s
unit-test (ubuntu-22.04)	37s
build (linux)	44s
unit-test (macos-latest)	34s
lint (linux)	43s
Build matrix	3s
integration-tests (change-entry-test.sh)	3m 28s
integration-tests (restore-entry-test.sh)	3m 18s
integration-tests (run-go-test.sh)	1m 46s
integration-tests (run-mysql-test.sh)	1m 50s
integration-tests (run-postgres-test.sh)	1m 55s
	16m 12s

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