perf(license): enable license classifier only with "--license-full"

[knqyf263]

Description

Initializing license classifiers and performing license classification is expensive and it is disabled by default. However, it is used only when scanning Debian because Debian licenses are not stored in a machine-readable format. In other words, scanning Debian activates the license classification and leads to high CPU/memory utilization.
This PR changes it to try to detect licenses without license classifiers by default and enable classifies only when --license-full is specified.

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[afdesk]

yes, this PR is really improve performance.

at first, I've run trivy v0.33.0.

$ trivy -v
Version: 0.33.0
Vulnerability DB:
  Version: 2
  UpdatedAt: 2022-10-27 12:08:13.914255809 +0000 UTC
  NextUpdate: 2022-10-27 18:08:13.914255509 +0000 UTC
  DownloadedAt: 2022-10-27 14:05:26.677439944 +0000 UTC

$ rm -r ~/.cache/trivy/fanal/ && trivy i perl:5.34.0

the maximum memory consumption was 511,2 MB:

then I've run the current branch:

$ ./tr -v
Version: dev
Vulnerability DB:
  Version: 2
  UpdatedAt: 2022-10-27 12:08:13.914255809 +0000 UTC
  NextUpdate: 2022-10-27 18:08:13.914255509 +0000 UTC
  DownloadedAt: 2022-10-27 14:05:26.677439944 +0000 UTC

$ rm -r ~/.cache/trivy/fanal/ && ./tr i perl:5.34.0

the maximum memory was 311MB: