[Test automation] generate custom test report (#739)

# What does this PR do?

Generate a test report in MD that contains two main infos: 
1)  custom report on inference provider -> API / functionalities
2) [TO BE ADDED] test log for easy debugging

## Test Plan
For local testing, run test script in command line. See a test report
being generated at tests/report.html

`pytest /Users/sxyi/llama-stack/llama_stack/providers/tests/.
--config=ci_test_config.yaml`

See
[gist](https://gist.github.com/sixianyi0721/a421fd3bc450b74354a1c2c7da483fa5)
for output MD file
## Sources

Please link relevant resources if necessary.


## Before submitting

- [ ] This PR fixes a typo or improves the docs (you can dismiss the
other checks if that's the case).
- [x] Ran pre-commit to handle lint / formatting issues.
- [x] Read the [contributor
guideline](https://github.com/meta-llama/llama-stack/blob/main/CONTRIBUTING.md),
      Pull Request section?
- [ ] Updated relevant documentation.
- [ ] Wrote necessary unit or integration tests.

llama_stack/providers/tests/conftest.py

@@ -21,6 +21,7 @@ from llama_stack.distribution.datatypes import Provider
 from llama_stack.providers.datatypes import RemoteProviderConfig
 
 from .env import get_env_or_fail
+from .report import Report
 
 
 class ProviderFixture(BaseModel):
@@ -140,6 +141,9 @@ def pytest_configure(config):
         key, value = env_var.split("=", 1)
         os.environ[key] = value
 
+    if config.getoption("--output") is not None:
+        config.pluginmanager.register(Report(config.getoption("--output")))
+
 
 def pytest_addoption(parser):
     parser.addoption(
@@ -155,6 +159,11 @@ def pytest_addoption(parser):
         action="store",
         help="Set test config file (supported format: YAML), e.g. --config=test_config.yml",
     )
+    parser.addoption(
+        "--output",
+        action="store",
+        help="Set output file for test report, e.g. --output=pytest_report.md",
+    )
     """Add custom command line options"""
     parser.addoption(
         "--env", action="append", help="Set environment variables, e.g. --env KEY=value"