chore(lambda-layer-proxyagent): autobump mechanism (#18788)

Add an autobump mechanism similar to the one in
#18780.


----

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

Author: rix0rrr

packages/@aws-cdk/lambda-layer-node-proxy-agent/.no-packagejson-validator

@@ -23,4 +23,4 @@ declare const fn: lambda.Function;
 fn.addLayers(new NodeProxyAgentLayer(this, 'NodeProxyAgentLayer'));
 ```
 
-[`proxy-agent`](https://www.npmjs.com/package/proxy-agent) will be installed under `/opt/nodejs/node_modules`.
+[`proxy-agent`](https://www.npmjs.com/package/proxy-agent) will be installed under `/nodejs/node_modules`.

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

@@ -1,8 +1,6 @@
 # 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
@@ -19,7 +17,8 @@ RUN yum update -y \
 #
 
 RUN mkdir -p /opt/nodejs
-RUN cd /opt/nodejs && npm install proxy-agent@${PROXY_AGENT_VERSION}
+COPY package*.json /opt/nodejs/
+RUN cd /opt/nodejs && npm ci && rm package*.json
 
 #
 # create the bundle

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

@@ -3,7 +3,7 @@ set -euo pipefail
 
 cd $(dirname $0)
 
-echo ">> Building AWS Lambda layer inside a docker image..."
+echo ">> Building AWS Lambda layer inside a docker image for Proxy Agent..."
 
 TAG='aws-lambda-node-proxy-agent'