test: Split inference tests to text and vision (#1008)

# What does this PR do?

This PR splits the inference tests into text and vision to make testing
on vLLM provider easier as mentioned in
https://github.com/meta-llama/llama-stack/pull/951 since serving
multiple models (e.g. Llama-3.2-11B-Vision-Instruct and
Llama-3.1-8B-Instruct) on a single port using the OpenAI API is [not
supported yet](https://docs.vllm.ai/en/v0.5.5/serving/faq.html) so it's
a bit tricky to test both at the same time.

## Test Plan

All previously passing tests related to text still pass:
`LLAMA_STACK_BASE_URL=http://localhost:5002 pytest -v
tests/client-sdk/inference/test_text_inference.py`

All vision tests passed via `LLAMA_STACK_BASE_URL=http://localhost:5002
pytest -v tests/client-sdk/inference/test_vision_inference.py`.

Signed-off-by: Yuan Tang <terrytangyuan@gmail.com>

.github/workflows/tests.yml

@@ -54,7 +54,7 @@ jobs:
           echo "REPORT_FILE=${REPORT_OUTPUT}" >> "$GITHUB_ENV"
 
           export INFERENCE_MODEL=meta-llama/Llama-3.1-8B-Instruct
-          LLAMA_STACK_CONFIG=./llama_stack/templates/${{ matrix.provider }}/run.yaml pytest --md-report --md-report-verbose=1 ./tests/client-sdk/inference/test_inference.py --md-report-output "$REPORT_OUTPUT"
+          LLAMA_STACK_CONFIG=./llama_stack/templates/${{ matrix.provider }}/run.yaml pytest --md-report --md-report-verbose=1 ./tests/client-sdk/inference/ --md-report-output "$REPORT_OUTPUT"
 
       - name: Output reports to the job summary
         if: always()