Add options to use playwright screenshot script for other things

In this case, storybook screenshots, but this keeps it so this script
doesnt know about storybook itself (we can move the actual storybook
specific code to here if we standardise on it more).

packages/element-web-playwright-common/playwright-screenshots.sh

@@ -1,25 +1,29 @@
 #!/bin/bash
+set -x
 
 # Handle symlinks here as we tend to be executed as an npm binary
 SCRIPT_PATH=$(readlink -f "$0")
 SCRIPT_DIR=$(dirname "$SCRIPT_PATH")
 
 IMAGE_NAME="element-web-playwright-common"
-echo "Building $IMAGE_NAME image in $SCRIPT_DIR"
 
-# Build image
-PW_VERSION=$(
-  yarn list \
-    --pattern @playwright/test \
-    --depth=0 \
-    --json \
-    --non-interactive \
-    --no-progress | \
-    jq -r '.data.trees[].name | split("@")[2]' \
-  )
-echo "with Playwright version $PW_VERSION"
+build_image() {
+  echo "Building $IMAGE_NAME image in $SCRIPT_DIR"
 
-docker build -t "$IMAGE_NAME" --build-arg "PLAYWRIGHT_VERSION=$PW_VERSION" "$SCRIPT_DIR"
+  # Build image
+  PW_VERSION=$(
+    yarn list \
+      --pattern @playwright/test \
+      --depth=0 \
+      --json \
+      --non-interactive \
+      --no-progress | \
+      jq -r '.data.trees[].name | split("@")[2]' \
+    )
+  echo "with Playwright version $PW_VERSION"
+
+  docker build -t "$IMAGE_NAME" --build-arg "PLAYWRIGHT_VERSION=$PW_VERSION" "$SCRIPT_DIR"
+}
 
 RUN_ARGS=(
   --rm
@@ -36,6 +40,35 @@ RUN_ARGS=(
   -it
 )
 
+DEFAULT_ARGS=(--grep @screenshot)
+
+# Some arguments to customise behaviour so the same script / image can be
+# re-used for other screenshot generation.
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    # Mounts a separate node_modules directory from a docker volume in the container.
+    # Must be used if executing something that requires native node modules
+    # It's a volume rather than a directory because otherwise things tend to start picking up
+    # files from it in the native environment and break.
+    --with-node-modules)
+      RUN_ARGS+=(--mount "type=volume,src=ew-docker-node-modules,dst=/work/node_modules,volume-nocopy")
+      shift
+      ;;
+    # Sets a different entrypoint (in which case the default arguments to the script will be ignored)
+    --entrypoint)
+      shift
+      RUN_ARGS+=(--entrypoint "$1")
+      DEFAULT_ARGS=()
+      shift
+      ;;
+    *)
+      break
+      ;;
+  esac
+done
+
+build_image
+
 # Ensure we pass all symlinked node_modules to the container
 pushd node_modules || exit > /dev/null
 SYMLINKS=$(find . -maxdepth 2 -type l -not -path "./.bin/*")
@@ -48,6 +81,4 @@ for LINK in $SYMLINKS; do
   fi
 done
 
-DEFAULT_ARGS=(--grep @screenshot)
-
-docker run "${RUN_ARGS[@]}" "$IMAGE_NAME" "${DEFAULT_ARGS[@]}" "$@"
+docker run "${RUN_ARGS[@]}" "$IMAGE_NAME" "${DEFAULT_ARGS[@]}" "$@"