Document Process for Creating Globus App for FuncX-Web-Service

_As a developer I want to be able to create my own globus apps that works so I can develop funcX locally_

## Acceptance Criteria
1. A README that shows the exact steps for setting up a confidential client app on developer.globus.org
2. Deploy a development funcX with the resulting client ID and secret
3. A README that shows the exact steps for creating a native app client
4. A new optional argument to the `FuncXClient` constructor where the developer can pass in a client ID
5. Developer can run demo code to connect to the local funcx service and it works

Start with the README requirements for confidential and native Globus client apps, then inspect the FuncXClient constructor and the demo code for local funcX. Verify the developer.globus.org setup steps, local deployment with the resulting credentials, optional client ID support, and a working local connection demo.

Written by the indexing model from the issue text.