Specify charset when using MySQL (#1059)

Because of backward-compatibility reasons, not specifying the charset
will result in "utf8" being used, which is a deprecated charset.
Also, when the charset for creating tables is not specified, the one
specified in the DSN is reused if specified.

In the future, DBAL is going to drop default values, which means we will
have to specify a charset anyway.

Author: greg0ire

doctrine/doctrine-bundle/2.3/manifest.json

@@ -11,7 +11,7 @@
         "#2": "IMPORTANT: You MUST configure your server version, either here or in config/packages/doctrine.yaml",
         "#3": "",
         "#4": "DATABASE_URL=\"sqlite:///%kernel.project_dir%/var/data.db\"",
-        "#5": "DATABASE_URL=\"mysql://db_user:db_password@127.0.0.1:3306/db_name?serverVersion=5.7\"",
+        "#5": "DATABASE_URL=\"mysql://db_user:db_password@127.0.0.1:3306/db_name?serverVersion=5.7&charset=utf8mb4\"",
         "DATABASE_URL": "postgresql://db_user:db_password@127.0.0.1:5432/db_name?serverVersion=13&charset=utf8"
     },
     "dockerfile": [

doctrine/doctrine-bundle/2.4/manifest.json

@@ -11,7 +11,7 @@
         "#2": "IMPORTANT: You MUST configure your server version, either here or in config/packages/doctrine.yaml",
         "#3": "",
         "#4": "DATABASE_URL=\"sqlite:///%kernel.project_dir%/var/data.db\"",
-        "#5": "DATABASE_URL=\"mysql://db_user:db_password@127.0.0.1:3306/db_name?serverVersion=5.7\"",
+        "#5": "DATABASE_URL=\"mysql://db_user:db_password@127.0.0.1:3306/db_name?serverVersion=5.7&charset=utf8mb4\"",
         "DATABASE_URL": "postgresql://symfony:ChangeMe@127.0.0.1:5432/app?serverVersion=13&charset=utf8"
     },
     "dockerfile": [