Drop the `position` column from the `security_findings` table

Why are we doing this work

We are in the process of deprecating the usage of the project_fingerprint attribute of the findings. By using uuid values to identify findings, we can easily associate any related entity with finding.

As we are going to use only the uuid column to identify findings, the position column is not needed anymore.

Dependency

• This issue has to be done after the release of #277332 (closed) so please make sure to start working on this after that dependency gets released.

Implementation plan

• backend Drop the position column from the security_findings table