[FE] Add Findings grouped by severity using REAL endpoint data

Context:

On the initial iteration we mock out the data in [FE] Fetch New Findings data from APi in data Provider and [FE] Fetch Fix Findings data from API in Data Provider due to the backend issue adding graphQL not being available.

This is a follow-up issue to consume/parse the real data returned from graphQL API and group findings into severities for the TreeView navigation in the left pane.

Implementation Plan:

TBD - Needs API Contract confirmation in [BE] Add public api endpoint for MR Vulnerability Findings