chore(build): allow generating a subset of language packages (aws#1730)

Update the build tools to take an argument to pack only a subset of language targets.

pack.sh

@@ -14,8 +14,9 @@ mkdir -p ${distdir}
 scopes=$(lerna ls 2>/dev/null | grep -v "(private)" | cut -d" " -f1 | xargs -n1 -I{} echo "--scope {}" | tr "\n" " ")
 
 # Run the "cdk-package" script in all modules. For jsii modules, this invokes jsii-pacmak which generates and builds multi-language
-# outputs. For non-jsii module, it will just run "npm pack" and place the output in dist/npm (which is similar to how pacmak outputs it).
-lerna run ${scopes} --sort --stream package
+# outputs. For non-jsii module, it will just run "npm pack" and place the output in dist/npm
+# (which is similar to how pacmak outputs it).
+lerna run ${scopes} --sort --stream package -- -- "$@"
 
 # Collect dist/ from all modules into the root dist/
 for dir in $(find packages -name dist | grep -v node_modules); do