Split off cli into separate binaries (#37)

* 🎨 Split off cli into separate binaries

This commit splits off the cli into 3 binaries:
- agent
- cli
- provider

The provider now is a separate component that can be tested by itself
and have its own lifecycle. This paves the way to a ligher c3os variant,
HA support and other features that can be provided on runtime.

This is working, but still there are low hanging fruit to care about.

Fixes #14

* 🤖 Add provider bin to releases

* ⚙️ Handle signals

* ⚙️ Reduce buildsize footprint

* 🎨 Scan for providers also in /system/providers

* 🤖 Run goreleaser

* 🎨 Refactoring

internal/utils/signal.go

@@ -0,0 +1,15 @@
+package utils
+
+import (
+	"os"
+	"os/signal"
+)
+
+func OnSignal(fn func(), sig ...os.Signal) {
+	sigs := make(chan os.Signal, 1)
+	signal.Notify(sigs, sig...)
+	go func() {
+		<-sigs
+		fn()
+	}()
+}