Add distro information into the CPE generation process

[alfredodeza]

What happened: Similarly to issue #94 - distros aren't currently considered when generating CPEs

What you expected to happen: Add distro information into the CPE generation process (https://github.com/anchore/grype/blob/main/grype/cpe/cpe.go#L69).

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

Environment:

• grype version (use grype version -v):
• OS (e.g: cat /etc/os-release or similar):

[wagoodman]

it isn't immediately clear what the value of adding distro information to CPEs would have to the matching process since we don't consider OS information when matching with CPEs.