Fix return type for fetchData

[magalimorin18]

What kind of change does this PR introduce (bug fix, feature, docs update, ...)?

Fix the type of the object returned by fetchData function.

What is the current behaviour (you can also link to an open issue here)?

When fetching profile await erc725.fetchData("LSP3Profile") expects that it will return DecodeDataOutput with value field. But value is typed as string | string[] | URLDataWithHash while in value I get profile object

{
LSP3Profile: 
{...}
}

Link to open issue

What is the new behaviour (if this is a feature change)?

A new type FetchDataOutput was created with the following properties :

FetchDataOutput {
  value:
    | string
    | string[]
    | { LSP3Profile: Record<string, any> }
    | Record<string, any>;
  name: string;
  key: string;
}

Closes #192

[Hugoo]

Closes #192