chore: allow to pass CA cert to remote vllm (#2266)

# What does this PR do?

The `tls_verify` can now receive a path to a certificate file if the
endpoint requires it.

Signed-off-by: Sébastien Han <seb@redhat.com>

llama_stack/providers/remote/inference/vllm/config.py

@@ -4,8 +4,9 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
+from pathlib import Path
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, field_validator
 
 from llama_stack.schema_utils import json_schema_type
 
@@ -24,11 +25,22 @@ class VLLMInferenceAdapterConfig(BaseModel):
         default="fake",
         description="The API token",
     )
-    tls_verify: bool = Field(
+    tls_verify: bool | str = Field(
         default=True,
-        description="Whether to verify TLS certificates",
+        description="Whether to verify TLS certificates. Can be a boolean or a path to a CA certificate file.",
     )
 
+    @field_validator("tls_verify")
+    @classmethod
+    def validate_tls_verify(cls, v):
+        if isinstance(v, str):
+            cert_path = Path(v)
+            if not cert_path.exists():
+                raise ValueError(f"TLS certificate file does not exist: {v}")
+            if not cert_path.is_file():
+                raise ValueError(f"TLS certificate path is not a file: {v}")
+        return v
+
     @classmethod
     def sample_run_config(
         cls,