Handle empty normalizer results

[Donnype]

Changes

Add an empty observation when nothing was found for an input ooi, to trigger deletion.

Issue link

Demo

QA notes

Please check deletion propagation for the SSL certificates (per the instructions of @noamblitz).

---

Code Checklist

• All the commits in this PR are properly PGP-signed and verified.
• This PR only contains functionality relevant to the issue.
• I have written unit tests for the changes or fixes I made.
• I have checked the documentation and made changes where necessary.
• I have performed a self-review of my code and refactored it to the best of my abilities.

---

Checklist for code reviewers:

Copy-paste the checklist from the docs/source/templates folder into your comment.

---

Checklist for QA:

Copy-paste the checklist from the docs/source/templates folder into your comment.

[noamblitz]

This fixes the issue!

[ammar92]

Looks good 👍 Tiny suggestion, but consider it approved.

[stephanie0x00]

Checklist for QA:

• I have checked out this branch, and successfully ran a fresh make reset.
• I confirmed that there are no unintended functional regressions in this branch:
  • I have managed to pass the onboarding flow
  • Objects and Findings are created properly
  • Tasks are created and completed properly
• I confirmed that the PR's advertised feature or hotfix works as intended.
• I checked the logs for errors and/or warnings and made issues where necessary

What works:

Seems to work using the reproduction steps mentioned by @noamblitz.

What doesn't work:

n/a

Bug or feature?:

n/a