feat: refactor external providers dir (#2049)

# What does this PR do?

currently the "default" dir for external providers is
`/etc/llama-stack/providers.d`

This dir is not used anywhere nor created.

Switch to a more friendly `~/.llama/providers.d/`

This allows external providers to actually create this dir and/or
populate it upon installation, `pip` cannot create directories in `etc`.

If a user does not specify a dir, default to this one

see https://github.com/containers/ramalama-stack/issues/36

Signed-off-by: Charlie Doern <cdoern@redhat.com>

.github/workflows/test-external-providers.yml

@@ -47,8 +47,8 @@ jobs:
 
       - name: Create provider configuration
         run: |
-          mkdir -p /tmp/providers.d/remote/inference
-          cp tests/external-provider/llama-stack-provider-ollama/custom_ollama.yaml /tmp/providers.d/remote/inference/custom_ollama.yaml
+          mkdir -p /home/runner/.llama/providers.d/remote/inference
+          cp tests/external-provider/llama-stack-provider-ollama/custom_ollama.yaml /home/runner/.llama/providers.d/remote/inference/custom_ollama.yaml
 
       - name: Build distro from config file
         run: |
@@ -66,7 +66,7 @@ jobs:
       - name: Wait for Llama Stack server to be ready
         run: |
           for i in {1..30}; do
-            if ! grep -q "remote::custom_ollama from /tmp/providers.d/remote/inference/custom_ollama.yaml" server.log; then
+            if ! grep -q "remote::custom_ollama from /home/runner/.llama/providers.d/remote/inference/custom_ollama.yaml" server.log; then
               echo "Waiting for Llama Stack server to load the provider..."
               sleep 1
             else