Add asdf support

**What would you like to be added**:

syft should add support for asdf. asdf is a generic package manager that can be used to install various tools. See https://github.com/asdf-vm/asdf

**Why is this needed**:

Using this syft may be able to capture versions of tools that are not currently captured by syft. Things like the version of python, ruby, node etc.

**Additional context**:

Start by reviewing Syft’s existing package-manager support and the asdf project linked in the issue. Determine how versions installed through asdf should be discovered and covered; done means Syft captures versions of tools such as Python, Ruby, and Node that it does not currently report.

Written by the indexing model from the issue text.