feat: add --providers to llama stack build (#1718)

# What does this PR do?

allow users to specify only the providers they want in the llama stack
build command. If a user wants a non-interactive build, but doesn't want
to use a template, `--providers` allows someone to specify something
like `--providers inference=remote::ollama` for a distro with JUST
ollama

## Test Plan

`llama stack build --providers inference=remote::ollama --image-type
venv`
<img width="1084" alt="Screenshot 2025-03-20 at 9 34 14 AM"
src="https://github.com/user-attachments/assets/502b5fa2-edab-4267-a595-4f987204a6a9"
/>

`llama stack run --image-type venv
/Users/charliedoern/projects/Documents/llama-stack/venv-run.yaml`
<img width="1149" alt="Screenshot 2025-03-20 at 9 35 19 AM"
src="https://github.com/user-attachments/assets/433765f3-6b7f-4383-9241-dad085b69228"
/>

---------

Signed-off-by: Charlie Doern <cdoern@redhat.com>
Signed-off-by: Sébastien Han <seb@redhat.com>
Co-authored-by: Sébastien Han <seb@redhat.com>

.github/workflows/providers-build.yml

@@ -81,3 +81,29 @@ jobs:
         run: |
           source test/bin/activate
           uv pip list
+
+  build-single-provider:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.10'
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v5
+        with:
+          python-version: "3.10"
+
+      - name: Install LlamaStack
+        run: |
+          uv venv
+          source .venv/bin/activate
+          uv pip install -e .
+
+      - name: Build a single provider
+        run: |
+          USE_COPY_NOT_MOUNT=true LLAMA_STACK_DIR=. uv run llama stack build --image-type venv --image-name test --providers inference=remote::ollama