title: select entity limit relation depth with manyToMany relation
body: <p>in my app, i have users.
  Each user has one Role (Admin, Tester, ...)
  each role can have several Permissions (homepage-view, contactpage-view ...)</p>
  
  <p>So, i have a ManyToMany relation</p>
  
  <p>Because i want to get Roles from permissions and permissions from roles, i have a bidirectionnal relation.</p>
  
  <p>What i want is just to select one permission with its roles</p>
  
  <p>My problem : when i get a permission, it gets each role with its permissions with its roles ...</p>
  
  <p>Result begin example :</p>
  
  <pre><code>{
    "id": 4,
    "nom": "Accès au backoffice",
    "slug": "page-backoffice",
    "role": [
      {
        "id": 1,
        "libelle": "Administrateur",
        "permission": [
          {
            "id": 3,
            "nom": "Visualisation du stock global",
            "slug": "page-visu-stock-global",
            "role": [
              {
                "id": 2,
                "libelle": "Responsable d'exploitation",
                "permission": [
                  {
                    .......
  </code></pre>
  
  <p>What i want is :</p>
  
  <pre><code>{
    "id": 4,
    "nom": "Accès au backoffice",
    "slug": "page-backoffice",
    "role": [
      {
        "id": 1,
        "libelle": "Administrateur",
        "slug": "administrateur"
      },
      {
        "id": 2,
        "libelle": "Responsable d'exploitation",
        "slug": "responsable-exploitation"
      },
      ....
  </code></pre>
  
  <p>How can i do it ?</p>
  
  <p>my orm file relation details :
  Permissions.orm.yml :</p>
  
  <pre><code>manyToMany:
      role:
          targetEntity: Role
          cascade: {  }
          fetch: LAZY
          mappedBy: permission
          inversedBy: null
          joinTable: null
          orderBy: null
  </code></pre>
  
  <p>role.orm.yml :</p>
  
  <pre><code> manyToMany:
      permission:
          targetEntity: Permissions
          cascade: {  }
          fetch: LAZY
          mappedBy: null
          inversedBy: role
          joinTable:
              name: role_permission
              joinColumns:
                  -
                      name: role_id
                      referencedColumnName: id
              inverseJoinColumns:
                  -
                      name: permission_id
                      referencedColumnName: id
          orderBy: null
  </code></pre>
  
  <p>Thanks for your help</p>