Retrieval Augmented Generation (RAG) at GitLab

What does this MR do and why?

This MR creates a new Blueprint for RAG at GitLab broadly, influenced heavily by the work done in the Retrieval Augmented Generation (RAG) for GitLab Duo MR, which was focused on Duo Chat specifically.

This blueprint is the first iteration for RAG solutions at GitLab and will be iterated upon

The following file structure exists:

blueprints
├── gitlab_rag
│   ├── index
│   ├── elasticsearch
│   ├── postgresql
│   └── vertex_ai_search
└── gitlab_duo_rag
    ├── index
    ├── elasticsearch
    ├── postgresql
    └── vertex_ai_search

Each folder contains evaluated and propsed implementations for general RAG and DUO documentation RAG respectively.