Makefile changes for nvm and acknowledge CDK issue #25674

[bharber-vr]

• Adds .nvmrc file. This pins the node.js version to 18, which is the current LTS version and the version supported by the CDK at this time. When the .nvmrc file is present in the current working directory, nvm will use that version for the nvm install and nvm use commands. This allows us to specify the node version in one place and reduce friction during the setup process.
• Modifies the Makefile commands to take advantage of nvm. nvm is already installed as a Homebrew dependency. The npx command allows us to use the CDK version installed in the node_modules directory of the blueprints app (vs relying on installing it globally and the versions potentially being out of sync)
• Acknowledges ‼️ NOTICE: eks overly permissive trust policies aws/aws-cdk#25674 This can be fixed by upgrading the CDK, however this needs to be tested