Add provider configuration which disables authentication

[chrismarget-j]

Proactive authentication happens here:

terraform-provider-apstra/apstra/provider.go

Lines 370 to 376 in d4dd621

	// Login after client creation so that future parallel
	// workflows don't trigger TOO MANY REQUESTS threshold.
	err = client.Login(ctx)
	if err != nil {
	resp.Diagnostics.AddError("apstra login failure", err.Error())
	return
	}

If we want to disable proactive authentication, we'll need a new provider configuration element.

WILL THIS EVEN WORK? -- disabling proactive authentication will only stop the first auth attempt. If we encounter a 401 response due to a problem in a pre-auth-ed proxy, the underlying library will still try to log in.