better support for installing plugins via composer (#5112)

* merge installation and update commands
* generate metadata from array
* new command to list available packages
* added a management script to simplify updates
* added directory for dev files
* helper functions for installation and listing of packages
* run plugin database installers

src/Plugin/Plugin.php

@@ -20,7 +20,7 @@ final class Plugin
     public function getMetadata(): PluginMetadata
     {
         if ($this->metadata === null) {
-            $this->metadata = new PluginMetadata($this->getPath());
+            $this->metadata = PluginMetadata::createFromPath($this->getPath());
         }
 
         return $this->metadata;
@@ -33,12 +33,7 @@ final class Plugin
 
     public function getName(): string
     {
-        $meta = $this->getMetadata();
-        if ($meta->getName() !== null) {
-            return $meta->getName();
-        }
-
-        return $this->getId();
+        return $this->getMetadata()->getName();
     }
 
     public function getId(): string