feat: add PSK for external provisionerd auth (#8877)

Signed-off-by: Spike Curtis <spike@coder.com>

cli/testdata/coder_server_--help.golden

@@ -373,6 +373,10 @@ updating, and deleting workspace resources.
       --provisioner-daemon-poll-jitter duration, $CODER_PROVISIONER_DAEMON_POLL_JITTER (default: 100ms)
           Random jitter added to the poll interval.
 
+      --provisioner-daemon-psk string, $CODER_PROVISIONER_DAEMON_PSK
+          Pre-shared key to authenticate external provisioner daemons to Coder
+          server.
+
       --provisioner-daemons int, $CODER_PROVISIONER_DAEMONS (default: 3)
           Number of provisioner daemons to create on start. If builds are stuck
           in queued state for a long time, consider increasing this.

cli/testdata/server-config.yaml.golden

@@ -327,6 +327,9 @@ provisioning:
   # Time to force cancel provisioning tasks that are stuck.
   # (default: 10m0s, type: duration)
   forceCancelInterval: 10m0s
+  # Pre-shared key to authenticate external provisioner daemons to Coder server.
+  # (default: <unset>, type: string)
+  daemonPSK: ""
 # Enable one or more experiments. These are not ready for production. Separate
 # multiple experiments with commas, or enter '*' to opt-in to all available
 # experiments.