Plugins: Add validation for plugin manifest (#52787)

* add validation for plugin manifest

* no more semver checking

* undo go.mod changes

* undo go.mod changes

* only validate v2 fields where necessary

* remove manifest version field check

pkg/plugins/models.go

@@ -177,10 +177,20 @@ type SignatureType string
 
 const (
 	GrafanaSignature     SignatureType = "grafana"
+	CommercialSignature  SignatureType = "commercial"
+	CommunitySignature   SignatureType = "community"
 	PrivateSignature     SignatureType = "private"
 	PrivateGlobSignature SignatureType = "private-glob"
 )
 
+func (s SignatureType) IsValid() bool {
+	switch s {
+	case GrafanaSignature, CommercialSignature, CommunitySignature, PrivateSignature, PrivateGlobSignature:
+		return true
+	}
+	return false
+}
+
 type PluginFiles map[string]struct{}
 
 type Signature struct {