connectOpts are ignored when upgrading socket connection to TLS

[joerg1985]

I need to set a client certificate to connect to our service, when using a proxy the connection fails.
new HttpsProxyAgent(process.env.HTTPS_PROXY, { pfx: buffer })

These connectOpts options are only used to connect, but when the connection is upgraded the connectOpts are ignored.

proxy-agents/packages/https-proxy-agent/src/index.ts

Lines 144 to 148 in e1e80ab

	return tls.connect({
	...omit(opts, 'host', 'path', 'port'),
	socket,
	servername: net.isIP(servername) ? undefined : servername,
	});

My perfered option would be to have second argument to the HttpsProxyAgent class with upgradeOpts.
new HttpsProxyAgent(process.env.HTTPS_PROXY, {}, { pfx: buffer })

When upgrading the connection these could be used with the regular options:

...omit(opts, 'host', 'path', 'port'),
...this.upgradeOpts,

With the new argument it would be even possible to connect to a https proxy with a client certificate and to the remote server with another client certificate. When using the original connectOpts setting a client certificate might disturb the connection to the proxy server.