Redesign `pkg/reporter` and `cmd/osv-reporter`

[cuixq]

Currently pkg/reporter is not well-designed and cmd/osv-reporter depends on it. We may get rid of current pkg/reporter in v2 and redesign both pkg/reporter and cmd/osv-scanner.

[another-rex]

Still to do, but not necessary for V2, changing from v2 to backlog. Specifically cmd/osv-reporter. pkg/reporter is needs to be done for V2, but is tracked elsewhere.

[G-Rath]

I'm going to call this done since while the package does still exist its now internal and just serves as a wrapper for output to handle some implementation details when translating from the "format" cli option into the actual function(s) (e.g. cyclonedx-<version> -> cycloneDXReporter{version: models.<version>}).