fix(lambda-layer-node-proxy-agent): Replace use of package.json with …

…Dockerfile command `npm install [package]@[version]` (#17078)

## Summary

This PR fixes an issue where the package.json file used in `lambda-layer-node-proxy-agent` was not being bundled into monocdk / CDK v2. This is due to limitations of Ubergen. Ubergen only copies .ts  files, README.md  files and some special .json files.

This PR:
- Removes the package.json from `packages/@aws-cdk/lambda-layer-node-proxy-agent/layer`
- Adds a step in the layer's Dockerfile to install a specific version of `proxy-agent` i.e. `npm install [package]@[version]`. This is so that we can do without the `package.json` file while still managing which version we bundle with the layer.

Fixes: #17061

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/lambda-layer-node-proxy-agent/layer/.dockerignore

@@ -1,2 +1 @@
 build.sh
-.no-packagejson-validator

packages/@aws-cdk/lambda-layer-node-proxy-agent/layer/Dockerfile

@@ -1,6 +1,8 @@
 # base lambda image
 FROM public.ecr.aws/lambda/nodejs:latest
 
+ARG PROXY_AGENT_VERSION=5.0.0
+
 USER root
 RUN mkdir -p /opt
 WORKDIR /tmp
@@ -17,8 +19,7 @@ RUN yum update -y \
 #
 
 RUN mkdir -p /opt/nodejs
-COPY package.json /opt/nodejs
-RUN cd /opt/nodejs && npm install
+RUN cd /opt/nodejs && npm install proxy-agent@${PROXY_AGENT_VERSION}
 
 #
 # create the bundle

packages/@aws-cdk/lambda-layer-node-proxy-agent/lib/node-proxy-agent-layer.ts

@@ -11,8 +11,8 @@ export class NodeProxyAgentLayer extends lambda.LayerVersion {
   constructor(scope: Construct, id: string) {
     super(scope, id, {
       code: lambda.Code.fromAsset(path.join(__dirname, 'layer.zip'), {
-        // we hash the package.json (it contains the tools versions) because hashing the zip is non-deterministic
-        assetHash: hashFile(path.join(__dirname, '..', 'layer', 'package.json')),
+        // we hash the Dockerfile (it contains the tools versions) because hashing the zip is non-deterministic
+        assetHash: hashFile(path.join(__dirname, '..', 'layer', 'Dockerfile')),
       }),
       description: '/opt/nodejs/node_modules/proxy-agent',
     });