fix(gen2-migration): tarball installation cannot find proxyAgent

[iliapolo]

Description of changes

Re-implement proxyAgent instead of calling provider.proxyAgent. In the dev branch, proxyAgent is not exported from the cloudformation provider package:

amplify-cli/packages/amplify-provider-awscloudformation/src/index.ts

Lines 216 to 218 in e366e6f

	formUserAgentParam,
	loadConfiguration,
	resolveRegion,

Since the gen2-migration tarball only packages the amplify-cli package, all other packages are consumed via normal dependencies that were published from the dev branch.

Note that in the gen2-migration branch, proxyAgent is exported since we added it:

amplify-cli/packages/amplify-provider-awscloudformation/src/index.ts

Lines 216 to 219 in 64edeeb

	formUserAgentParam,
	loadConfiguration,
	resolveRegion,
	proxyAgent,

Meaning that when we merge gen2-migration with dev, we can remove this.

The implementation of proxyAgent came from here:

amplify-cli/packages/amplify-provider-awscloudformation/src/aws-utils/aws-globals.ts

Lines 1 to 10 in e366e6f

	import { ProxyAgent } from 'proxy-agent';
	export const proxyAgent = () => {
	let httpAgent = undefined;
	const httpProxy = process.env.HTTP_PROXY || process.env.HTTPS_PROXY;
	if (httpProxy) {
	httpAgent = new ProxyAgent();
	}
	return httpAgent;
	};

Issue #, if available

#14754

Description of how you validated changes

1. Build and install the local tarball
2. Ran npx amplify gen2-migration asses

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies
• Pull request labels are added

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