Add the ability to add attributes to sketches

[kiddinn]

Attributes need to be key/value pairs in the DB schema.

This could be used to denote SIEM/SEM/ticketing system ticket numbers, references to case notes, or something else that is relevant to the investigation/sketch.

This means that we need to add:

• [ ] Change the DB schema, add a class called Attribute
• [ ] Change the sketch schema to add a 1:many relationship, attributes
• [ ] Add an API to add/remove/edit attributes in a sketch
• [ ] Add support for the new API call into the API client.

Then finally this needs to be added to the UI