test: add e2e tests with local Forgejo instance (#201)

* feat(forge): add new forge for forgejo

We only support repositories hosted on Forgejo instances, but not
Forgejo Actions or Woodpecker as CI solutions for now.

* test(e2e): introduce e2e test framework with local forgejo

test/e2e/forge.go

@@ -0,0 +1,19 @@
+package e2e
+
+import (
+	"context"
+	"testing"
+)
+
+type TestForge interface {
+	Init(ctx context.Context, runID string) error
+	CreateRepo(t *testing.T, opts CreateRepoOpts) (*Repository, error)
+
+	RunArguments() []string
+}
+
+type CreateRepoOpts struct {
+	Name          string
+	Description   string
+	DefaultBranch string
+}