Improve PR diff scan

[attiasas]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• This pull request is on the dev branch.
• I used gofmt for formatting the code before submitting the pull request.
• Update documentation about new features / new supported technologies

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Depends on:

• Add 'Title' attribute to PR information froggit-go#148
• Diff scan jfrog-cli-security#389

[github-actions]

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🐸 JFrog Frogbot

[orz25]

Writing the e2e test scenarios to add:

1. Target branch has no issues, source branch has no issues -> no issues.
2. Target branch has no issues, source branch has some issues -> all source branch issues.
3. Target branch has some issues, source branch has no new issues -> no issues.
4. Target branch has some issues, source branch has new issues -> only new issues from source branch.