Enhance code commit collection capabilities for VCIO

[TG1999]

• For VCS URLs that can be formed into PURLs as of today, (github, bitbucket anf gitlab). We will support them for code commit collection
• For the types that we don't support, we will not create CodeCommits for them today, instead store them as references for now as a fallback
• We will also log these kind of commits
• We will have an improver that takes references with the advisories associated and tries to create valid code commits
• Later when improve our parsing capabilities in url2purl for various VCS URL types, this improver will handle the rest
• We will also store the commit diffs in our models

fixed_by_commits = [CommitV2(commit_hash="abcd", vcs_url="github/...")] 
affected_commits = [CommitV2(commit_hash="abcd", vcs_url="github/...")] 
affected_packages = [ AffectedPackageV2( package=purl, fixed_by_commits=fixed_commits, affected_by_commits=affected_commits, ) ] 

yield AdvisoryData( aliases=[vuln_id], affected_packages=[affected_packages], references=sorted(references), date_published=date_published, url=self.data_url, )

• This is the valid design
• We will introduce, fixed_by_commits, introduced_by_commits
• And for an affectedPackage dataclass object to be valid, it needs to have either of one affected_by_commits, fixed_by_commits, affecting_range or fixed_by_range.

Reference:

• Add support for introduced and fixed commits in AdvisoryData #2017
• fedcode-next: Code pipeline and models to continuously automatically collect fix commits #1721
• Add new model to store code fixes #2010

[TG1999]

• commit rank should be in unique together
• get rid of author, message and date
• commit_patch = models.TextField(
  null=True, blank=True, help_text="patch content of the commit."
  )
• Rename CodeCommit model to CodePatch

[TG1999]

• commit_patch_hash = models.TextField(
  null=True, blank=True, help_text="patch content of the commit."
  )

We can introduce commit patch hash later

• Just commit.
• Just patch.
• Both commit and patch.

We need to define a way to store unique contents for patches.