Add support for SPIFFE_ENDPOINT_SOCKET, deprecate SPIRE_AGENT_ADDRESS #486

Job	Run time
cache-deps (linux)	18s
build-images	1m 0s
lint (linux)	52s
build (linux)	49s
unit-test (ubuntu-22.04)	41s
unit-test (macos-latest)	29s
Build matrix	3s
integration-tests (change-entry-test.sh)	3m 32s
integration-tests (restore-entry-test.sh)	3m 25s
integration-tests (run-go-test.sh)	2m 1s
integration-tests (run-mysql-test.sh)	2m 9s
integration-tests (run-postgres-test.sh)	2m 17s
	17m 36s

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