fix: resolve ARG scope and variable quoting issues in Dockerfile

- Moved the ARG instruction inside the build stage where it is used.
- Surrounded $ASYNCAPI_GENERATOR_VERSION with double quotes to prevent word splitting and globbing issues.
- Improved maintainability and reliability by ensuring proper variable handling.

apps/generator/Dockerfile

@@ -1,18 +1,18 @@
-ARG ASYNCAPI_GENERATOR_VERSION=1.10.9
-
 FROM node:18-alpine
 
+ARG ASYNCAPI_GENERATOR_VERSION="1.10.9"  # Include ARG in the build stage and surround it with double quotes
+
 WORKDIR /app
 
 # Since 0.14.0 release of html-template chromium is needed for pdf generation
-ENV PUPPETEER_EXECUTABLE_PATH /usr/bin/chromium-browser
-ENV PUPPETEER_SKIP_CHROMIUM_DOWNLOAD true
+ENV PUPPETEER_EXECUTABLE_PATH="/usr/bin/chromium-browser"
+ENV PUPPETEER_SKIP_CHROMIUM_DOWNLOAD="true"
 
 # Since 0.30.0 release Git is supported and required as a dependency
 # Since 0.14.0 release of html-template chromium is needed for pdf generation.
 # More custom packages for specific template should not be added to this dockerfile. Instead, we should come up with some extensibility solution.
 RUN apk --update add --no-cache git chromium && \
-    npm install -g @asyncapi/generator@$ASYNCAPI_GENERATOR_VERSION && \
+    npm install -g @asyncapi/generator@"$ASYNCAPI_GENERATOR_VERSION" && \  # Surround variable with double quotes
     npm cache clean --force
 
 # Define the entry point for the AsyncAPI generator