Add Default Credentials Mapping

[mr-pmillz]

Is your feature request related to a problem? Please describe.

Add a default credentials mapping based on source html/response data.
This feature is not a huge priority but would be pretty sweet.

Describe the solution you'd like

EyeWitness uses txt files for signatures / categories and regex to do this mapping, but we could use a struct to json or yaml fingerprints file as an alternative approach.

In the GoWitness report, there could be a default credentials indicator icon in the gallery and additional info in the singular report page sections.

Additional context
Created this issue as a potential feature / todo list item.

[leonjza]

Great idea. I was wondering about exactly this thing recently looking at this repo: https://github.com/ihebski/DefaultCreds-cheat-sheet (which is also permissively licensed!), but I left it thinking the false positive rate may be too high. However, the idea of more accurate fingerprints actually sounds great!

My preference would be a more structured data source too.