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

tests/phpstan.neon

@@ -729,11 +729,6 @@ parameters:
             count: 1
             path: Command/PromoteUserCommandTest.php
 
-        -
-            message: "#^Cannot call method getConnection\\(\\) on object\\|null\\.$#"
-            count: 1
-            path: Command/UpdateCommandTest.php
-
         -
             message: "#^Method App\\\\Tests\\\\Command\\\\VersionCommandTest\\:\\:getCommandTester\\(\\) has parameter \\$options with no value type specified in iterable type array\\.$#"
             count: 1