Elastic search index not updated when reporter is anonymized

[4c0n]

Description

Currently the elastic search index is not updated when a reporter is anonymized. This PR aims to resolve that problem by sending a Django signal and handling it in a receiver that triggers a celery task to re-index the signal in the elastic search index.

Checklist

• Keep the PR, and the amount of commits to a minimum
• The commit messages are meaningful and descriptive
• The change/fix is well documented, particularly in hard-to-understand areas of the code / unit tests
• Are there any breaking changes in the code, if so are they discussed and did the team agreed to these changes
• Check that the branch is based on main and is up to date with main
• Check that the PR targets main
• There are no merge conflicts and no conflicting Django migrations

How has this been tested?

• Provided unit tests that will prove the change/fix works as intended
• Tested the change/fix locally and all unit tests still pass
• Code coverage is at least 85% (the higher the better)
• No iSort, Flake8 and SPDX issues are present in the code