text: Title: Put all docarray method in document and da into a common namespace
  Body: # context
  
  as we allow flexible schema we need a way to prevent user to use a key name that is already used by docarray. The best way to do it is to have a namespace for al of the method of `Document`. 
  
  Example:
  
  `doc.from_protobuf -> doc.doc_from_protobuf`
  
  or 
  
  `doc.da_from_protobuf`
  
  then we just need to tell the user you cannot have a key name that start with `doc` as it is reserved for docarray method.
  
  Pydantic v2 will have a similar approach : https://docs.pydantic.dev/blog/pydantic-v2/#model-namespace-cleanup