fix: Add SIGHUP and SIGTERM handling to coder server (#3543)

* fix: Add `SIGHUP` and `SIGTERM` handling to `coder server`

To prevent additional signals from aborting program execution, signal
handling was moved to the beginning of the main function, this ensures
that signals stays registered for the entire shutdown procedure.

Fixes #1529

cli/signal_unix.go

@@ -0,0 +1,14 @@
+//go:build !windows
+
+package cli
+
+import (
+	"os"
+	"syscall"
+)
+
+var interruptSignals = []os.Signal{
+	os.Interrupt,
+	syscall.SIGTERM,
+	syscall.SIGHUP,
+}