Use pip build cache from inside Dockerfile (#3228)

Dockerfile

@@ -23,13 +23,24 @@ WORKDIR /install
 
 COPY requirements.txt /requirements.txt
 
-# --extra-index-url https://www.piwheels.org/simple  is for cryptography module to be prebuilt (or rustc etc needs to be installed)
-RUN pip install --extra-index-url https://www.piwheels.org/simple  --target=/dependencies -r /requirements.txt
+# Use cache mounts and multiple wheel sources for faster ARM builds
+ENV PIP_CACHE_DIR=/tmp/pip-cache
+RUN --mount=type=cache,target=/tmp/pip-cache \
+    pip install \
+    --extra-index-url https://www.piwheels.org/simple \
+    --extra-index-url https://pypi.anaconda.org/ARM-software/simple \
+    --cache-dir=/tmp/pip-cache \
+    --target=/dependencies \
+    -r /requirements.txt
 
 # Playwright is an alternative to Selenium
 # Excluded this package from requirements.txt to prevent arm/v6 and arm/v7 builds from failing
 # https://github.com/dgtlmoon/changedetection.io/pull/1067 also musl/alpine (not supported)
-RUN pip install --target=/dependencies playwright~=1.48.0 \
+RUN --mount=type=cache,target=/tmp/pip-cache \
+    pip install \
+    --cache-dir=/tmp/pip-cache \
+    --target=/dependencies \
+    playwright~=1.48.0 \
     || echo "WARN: Failed to install Playwright. The application can still run, but the Playwright option will be disabled."
 
 # Final image stage