Move doctrine/doctrine-bundle requirement under require-dev (#493)

* Move doctrine/doctrine-bundle requirement under require-dev

The doctrine/doctrine-bundle seems to only be used by tests:
https://github.com/search?q=repo%3Alexik%2FLexikTranslationBundle%20Doctrine%5CBundle&type=code

This PR moves the requirement under require-dev so that I can install doctrine-bundle v3 in my project:

```
  Problem 1
    - Root composer.json requires lexik/translation-bundle ^7.3 -> satisfiable by lexik/translation-bundle[v7.3, ..., v7.3.6].
    - lexik/translation-bundle[v7.3, ..., v7.3.6] require doctrine/doctrine-bundle ^2.2 -> found doctrine/doctrine-bundle[2.2.0, ..., 2.18.2] but it conflicts with your root composer.json require (^3.2).
```

* Add symfony/var-exporter dependency to composer.json

Author: nicodemuz

composer.json

@@ -23,7 +23,6 @@
     ],
     "require": {
         "php": "^8.1|^8.2|^8.3|^8.4",
-        "doctrine/doctrine-bundle": "^2.2",
         "doctrine/orm": "^3",
         "monolog/monolog": "^3.2",
         "symfony/asset": "^7.0|^8.0",
@@ -41,6 +40,7 @@
         "doctrine/annotations": "^2",
         "doctrine/cache": "^1.4|^2.0",
         "doctrine/data-fixtures": "^1.1|^2.0",
+        "doctrine/doctrine-bundle": "^2.2",
         "doctrine/mongodb-odm": "^2.7",
         "doctrine/mongodb-odm-bundle": "^5.0",
         "mikey179/vfsstream": "^1.6",