Resolve "Rename Vulnerabilities::Findings::CreateFromSecurityFindingService"

What does this MR do and why?

Rename the Vulnerabilities::Findings::CreateFromSecurityFindingService and Vulnerabilities::CreateFromSecurityFindingService services to be more semantically meaningful. Also remove a redundant vulnerability_finding presence check from the newly named Vulnerabilities::FindOrCreateFromSecurityFindingService.

Rubocop also flagged this code as being in contravention of it's cops now, so I've applied it's automated changes.

How to set up and validate locally

Nothing should be functionally affected by this change.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #366656