docs: Updated docs to show minimal RAG example and some other minor changes (#1935)

# What does this PR do?
Incorporating some feedback into the docs.

- **`docs/source/getting_started/index.md`:**
    - Demo actually does RAG now
    - Simplified the installation command for dependencies.
    - Updated demo script examples to align with the latest API changes.
- Replaced manual document manipulation with `RAGDocument` for clarity
and maintainability.
- Introduced new logic for model and embedding selection using the Llama
Stack Client SDK.
- Enhanced examples to showcase proper agent initialization and logging.
- **`docs/source/getting_started/detailed_tutorial.md`:**
- Updated the section for listing models to include proper code
formatting with `bash`.
    - Removed and reorganized the "Run the Demos" section for clarity.
- Adjusted tab-item structures and added new instructions for demo
scripts.
- **`docs/_static/css/my_theme.css`:**
- Updated heading styles to include `h2`, `h3`, and `h4` for consistent
font weight.
- Added a new style for `pre` tags to wrap text and break long words,
this is particularly useful for rendering long output from generation.

    
## Test Plan
Tested locally. Screenshot for reference:

<img width="1250" alt="Screenshot 2025-04-10 at 10 12 12 PM"
src="https://github.com/user-attachments/assets/ce1c8986-e072-4c6f-a697-ed0d8fb75b34"
/>

---------

Signed-off-by: Francisco Javier Arceo <farceo@redhat.com>

docs/_static/css/my_theme.css

@@ -17,9 +17,13 @@
     display: none;
 }
 
-h3 {
+h2, h3, h4 {
     font-weight: normal;
 }
 html[data-theme="dark"] .rst-content div[class^="highlight"] {
   background-color: #0b0b0b;
 }
+pre {
+    white-space: pre-wrap !important;
+    word-break: break-all;
+}