[Backend] Update secrets push check to exclude based on existing exclusions

Overview

This issue tracks the work required to have the secrets push check load, and handle existing exclusions for a certain project.

The expectation is that the push check will perform the following actions (marked ones are already performed):

• Project Eligibility Check ✅
• Payload Retrieval (whether those payloads are entire blobs or diffs). ✅
• Project Security Exclusions Retrieval
• Run Scanning Engine (i.e. Gem or SDS) with Payloads + Exclusions Data
• Format and Display Scan Results ✅

Implementation Plan

Below is a list of tasks to perform in order to achieve the desired outcome of this issue.

• Update secrets push check to retrieve exclusions data from the database.
• Update secrets push check to run scanning engines with payload and exclusions data.
• Update corresponding tests to confirm the behaviour works as intended.