Support exporting license and copyright information in debian copyright format to integrate with REUSE

## Short Description

In order to use results from scancode in projects adopting REUSE [1] it would be nice if copyright and license information could be exported in debian copyright format [2] which is used in REUSE for non-intrusive bulk licensing. This is useful
e.g. in projects implemented in golang where source code of dependencies is pulled into the `vendor/` folder of the
project's repository.

[1] https://reuse.software/faq/#bulk-license
[2] https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/#disclaimer-field

## Possible Labels

- new feature
- enhancement
- integration
- plugin

## Select Category

- [ x ] Enhancement
- [ ] Add License/Copyright
- [ ] Scan Feature
- [ ] Packaging
- [ ] Documentation
- [ ] Expand Support
- [ x ] Other

## **Describe the Update**

Export of copyright and license information in debian copyright format which is used by REUSE.

## **How This Feature will help you/your organization**

Automate compliance with REUSE especially for golang projects which tend to have
a lot of (source code of) dependencies in the `vendor/` folder. Both creation of initial
`.reuse/dep5` file and updating it whenever dependencies change in order to declare copyright
and license information for such dependencies is a lot of work when done manually.

We currently use a poor-man's partial solution using askalono which can only generate
the `Files:` and `License:` fields of debian copyright format.

## **Possible Solution/Implementation Details**

Without knowing any details about scancode's implementation I guess this could
be implemented as a post scan plugin.

## **Example/Links if Any**

## **Can you help with this Feature**

I am python 3 literate so I could try to help if you can provide hints how to start that.
I have no clue about the current scancode-toolkit implementation.