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/github/releases.go

@@ -0,0 +1,49 @@
+package github
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"net/http"
+	"strings"
+
+	"github.com/google/go-github/v40/github"
+	"golang.org/x/oauth2"
+)
+
+func newHTTPClient(ctx context.Context, token string) *http.Client {
+	if token == "" {
+		return http.DefaultClient
+	}
+	src := oauth2.StaticTokenSource(&oauth2.Token{AccessToken: token})
+	return oauth2.NewClient(ctx, src)
+}
+
+func FindReleases(ctx context.Context, token, slug string) ([]string, error) {
+	hc := newHTTPClient(ctx, token)
+	cli := github.NewClient(hc)
+
+	repo := strings.Split(slug, "/")
+	if len(repo) != 2 || repo[0] == "" || repo[1] == "" {
+		return nil, fmt.Errorf("Invalid slug format. It should be 'owner/name': %s", slug)
+	}
+
+	rels, res, err := cli.Repositories.ListReleases(ctx, repo[0], repo[1], nil)
+	if err != nil {
+		log.Println("API returned an error response:", err)
+		if res != nil && res.StatusCode == 404 {
+			// 404 means repository not found or release not found. It's not an error here.
+			err = nil
+			log.Println("API returned 404. Repository or release not found")
+		}
+		return nil, err
+	}
+
+	versions := []string{}
+	for _, rel := range rels {
+		if strings.HasPrefix(*rel.Name, "v") {
+			versions = append(versions, *rel.Name)
+		}
+	}
+	return versions, nil
+}