Create and run workflows within a namespace

Allow a user to add workflows with the same name by implementing the namespace feature.
The idea has similarities to workbooks, but it doesn't forces the user to merge all it's workflows to one file.

Also, during execution create the user will not have to concatenate the namespace to the workflow name and just pass it as another parameter.

Some kind of a new parameter will be added both to the create workflow-definition request and to the create execution request. This new parameter should specify the namespace. In the case of create execution request the parameter might be a part of env (should be decided when working on the spec).