misc fixes for Thirdparty / addPerson

* set default values for ThirdParty in ThirdParty.vue
* set correct value for binding with phone (telephone instead of
phonenumber)
* add validation on ThirdParty/denomination: at least two characters, no
Null value

src/Bundle/ChillThirdPartyBundle/Entity/ThirdParty.php

@@ -179,6 +179,8 @@ class ThirdParty implements TrackCreationInterface, TrackUpdateInterface
      * @var string
      * @ORM\Column(name="name", type="string", length=255)
      * @Assert\Length(min="2")
+     * @Assert\NotNull
+     * @Assert\NotBlank
      * @Groups({"read", "write", "docgen:read", "docgen:read:3party:parent"})
      */
     private ?string $name = '';