Configure Systemd Socket Activation

as new way for Poseidon to accept connections. This should reduce our issues caused by deployments.

.github/workflows/resources/poseidon-minimal.service

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+# This is a minimal service definition to make use of the systemd socket activation in the e2e tests.
+# With Systemd socket activation, systemd sets up a listening socket on behalf of a service.
+# This is useful for zero downtime deployments as the systemd sockets hold up the connections while the service is restarting.
+
+[Unit]
+Requires=poseidon.socket
+
+[Service]
+WorkingDirectory=${GITHUB_WORKSPACE}
+ExecStart=${GITHUB_WORKSPACE}/poseidon
+Restart=always
+Environment="POSEIDON_SERVER_SYSTEMDSOCKETACTIVATION=TRUE"

.github/workflows/resources/poseidon-minimal.socket

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+# This is a minimal socket definition to provide a systemd socket for the Poseidon e2e tests.
+
+[Socket]
+ListenStream = 7200