feat(tests): migrate to global "setups" system for test configuration (#3390)

This PR refactors the integration test system to use global "setups"
which provides better separation of concerns:

**suites = what to test, setups = how to configure.**

NOTE: if you naming suggestions, please provide feedback

Changes:
- New `tests/integration/setups.py` with global, reusable configurations
(ollama, vllm, gpt, claude)
- Modified `scripts/integration-tests.sh` options to match with the
underlying pytest options
    - Updated documentation to reflect the new global setup system

The main benefit is that setups can be reused across multiple suites
(e.g., use "gpt" with any suite) even though sometimes they could
specifically tailored for a suite (vision <> ollama-vision). It is now
easier to add new configurations without modifying existing suites.

Usage examples:
    - `pytest tests/integration --suite=responses --setup=gpt`
- `pytest tests/integration --suite=vision` # auto-selects
"ollama-vision" setup
    - `pytest tests/integration --suite=base --setup=vllm`

.github/actions/setup-ollama/action.yml

@@ -1,7 +1,7 @@
 name: Setup Ollama
 description: Start Ollama
 inputs:
-  test-suite:
+  suite:
     description: 'Test suite to use: base, responses, vision, etc.'
     required: false
     default: ''
@@ -11,7 +11,7 @@ runs:
     - name: Start Ollama
       shell: bash
       run: |
-        if [ "${{ inputs.test-suite }}" == "vision" ]; then
+        if [ "${{ inputs.suite }}" == "vision" ]; then
           image="ollama-with-vision-model"
         else
           image="ollama-with-models"