`ApplicationManifestUtilsV3#write` is not threadsafe

[LitschiW]

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.

[JNKielmann]

We are encountering the same issue while deploying multiple apps simultaneously and would greatly appreciate a solution as well.