FEAT Metadata for datasets should allow fields as string OR list of strings

[romanlutz]

Currently, we accept only string. This issue is to investigate whether we can allow string OR a list of authors as detailed in the post below:
 
Originally posted by Raja Sekhar Rao Dheekonda (@rdheekonda) in https://github.com/Azure/PyRIT/pull/210#discussion_r1669316779

Same applies for other fields:
https://github.com/Azure/PyRIT/pull/210#discussion_r1669316935

[romanlutz]

#396 addressed this.