`ApplicationManifestUtilsV3#write` is not threadsafe

The method ApplicationManifestUtilsV3#write uses a static snakeyaml Yaml dumper to write all manifests into a byte array. This operation is inheritly not threadsafe, as the deserializer is not.

This in itself may not a be problem. However, when using Applications#pushManifestv3 to push multiple Apps in parallel this can cause issues that manifest in the form of

• Bad request: Manifest does not support Anchors and Aliases or
• java.lang.NullPointerException: Nodes must be provided.

Snakeyaml recommends to create a singe instance per thread.

Comienza con ApplicationManifestUtilsV3#write y el uso de Snakeyaml descrito en el issue; después, sigue las llamadas desde Applications#pushManifestv3. Reproduce pushes de manifiestos en paralelo y observa los errores de anchor/alias o de puntero nulo reportados. La tarea estará terminada cuando los pushes concurrentes se completen sin esos errores y el comportamiento esté cubierto por una prueba adecuada.