feat(output): Only fail secret scans when the secret is introduced

[Walz]

Context

Related to SPI-526 and will close #1001

We want to only fail secret scans when the secret is introduced.
New fields have been added to the API to automatically detect if the content is a diff and if the secret has been added, deleted or in the context. (GitGuardian/py-gitguardian#122)

• Add not_introduced as an ignore reason
• Make use of diff_kind to ignore policy breaks

diff_kind can be null (outside of commit) or ADDITION/DELETION/CONTEXT. We want to keep only the policy breaks with diff_kind:

• null => outside of commits, when scanning files or docker layers
• ADDITION => introduced by a commit

In #1024, a --all-secrets option will allow user to display ignored secrets.

Validation

• Create a repository
• Add a secret in commit A
• Edit the line below the secret in commit B
• Remove the secret in commit C

When scanning the repository with main: 3 policy breaks are found in commit A, B and C
When scanning with this PR: 1 policy break is found in commit A

PR check list

• As much as possible, the changes include tests (unit and/or functional)
• If the changes affect the end user (new feature, behavior change, bug fix) then the PR has a changelog entry (see doc/dev/getting-started.md). If the changes do not affect the end user, then the skip-changelog label has been added to the PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.03%. Comparing base (6427d8f) to head (b34d264).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1010   +/-   ##
=======================================
  Coverage   92.03%   92.03%           
=======================================
  Files         181      181           
  Lines        7706     7708    +2     
=======================================
+ Hits         7092     7094    +2     
  Misses        614      614           

Flag	Coverage Δ
unittests	92.03% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Walz]

Thanks to #1016, this PR is a lot simpler now.

[gitguardian]

️✅ There are no secrets present in this pull request anymore.

If these secrets were true positive and are still valid, we highly recommend you to revoke them.
Once a secret has been leaked into a git repository, you should consider it compromised, even if it was deleted immediately.
Find here more information about risks.

---

^{_{🦉 GitGuardian detects secrets in your source code to help developers and security teams secure the modern development process. You are seeing this because you or someone else with access to this repository has authorized GitGuardian to scan your pull request.}}

[agateau-gg]

Nice! And thanks for the great PR description ✨.