RHAIENG-948: fix(ppc): build failure due to missing numpy>=1.16.6 in aipcc wheel index

```
+ pip install --no-cache-dir /tmp/wheels/pyarrow-17.0.0-cp312-cp312-linux_ppc64le.whl
Looking in indexes: https://console.redhat.com/api/pypi/public-rhai/rhoai/3.0/cpu-ubi9/simple/
Processing /tmp/wheels/pyarrow-17.0.0-cp312-cp312-linux_ppc64le.whl
INFO: pip is looking at multiple versions of pyarrow to determine which version is compatible with other requirements. This could take a while.
ERROR: Could not find a version that satisfies the requirement numpy>=1.16.6 (from pyarrow) (from versions: none)
ERROR: No matching distribution found for numpy>=1.16.6
```

Author: jiridanek

jupyter/datascience/ubi9-python-3.12/Dockerfile.cpu

@@ -337,7 +337,8 @@ COPY --from=pyarrow-builder /tmp/wheels /tmp/wheels
 RUN /bin/bash <<'EOF'
 set -Eeuxo pipefail
 if [ "$TARGETARCH" = "ppc64le" ] || [ "$TARGETARCH" = "s390x" ]; then
-    pip install --no-cache-dir /tmp/wheels/*.whl
+    # aipcc is lacking numpy>=1.16.6
+    pip install --no-cache-dir --extra-index-url https://pypi.org/simple /tmp/wheels/*.whl
 else
     echo "Skipping wheel install for $TARGETARCH"
 fi
@@ -351,7 +352,8 @@ COPY --from=onnx-builder /root/onnx_wheel/ /onnxwheels/
 RUN /bin/bash <<'EOF'
 set -Eeuxo pipefail
 if [ "${TARGETARCH}" = "ppc64le" ]; then
-    pip install --no-cache-dir /onnxwheels/*.whl
+    # aipcc is sure to lack something, so add extra index preemptively
+    pip install --no-cache-dir --extra-index-url https://pypi.org/simple /onnxwheels/*.whl
 else
     echo "Skipping ONNX/OpenBLAS install on non-Power"
 fi

jupyter/datascience/ubi9-python-3.12/Dockerfile.konflux.cpu

@@ -337,7 +337,8 @@ COPY --from=pyarrow-builder /tmp/wheels /tmp/wheels
 RUN /bin/bash <<'EOF'
 set -Eeuxo pipefail
 if [ "$TARGETARCH" = "ppc64le" ] || [ "$TARGETARCH" = "s390x" ]; then
-    pip install --no-cache-dir /tmp/wheels/*.whl
+    # aipcc is lacking numpy>=1.16.6
+    pip install --no-cache-dir --extra-index-url https://pypi.org/simple /tmp/wheels/*.whl
 else
     echo "Skipping wheel install for $TARGETARCH"
 fi
@@ -351,7 +352,8 @@ COPY --from=onnx-builder /root/onnx_wheel/ /onnxwheels/
 RUN /bin/bash <<'EOF'
 set -Eeuxo pipefail
 if [ "${TARGETARCH}" = "ppc64le" ]; then
-    pip install --no-cache-dir /onnxwheels/*.whl
+    # aipcc is sure to lack something, so add extra index preemptively
+    pip install --no-cache-dir --extra-index-url https://pypi.org/simple /onnxwheels/*.whl
 else
     echo "Skipping ONNX/OpenBLAS install on non-Power"
 fi