Documentation lacks HTEx and Config

[WardLT]

Is your feature request related to a problem? Please describe.
Setting up an endpoint was complicated by some key details being hard to find in the documentation:

• HighThroughputExecutor is not listed in the autodocs
• Config file is not listed in the autodocs either

Both these made figuring out how to configure my application difficult, although that was benefited by the example configuration for Theta. However,

• The example documentation for Theta references a "~/setup_funcx_test_env.sh" that is not listed in the documentation.
• You should also provide general advice for making sure workers have the correct Python environments. E.g., is this given in the worker activitation, when launching the FuncX endpoint, etc?

Describe the solution you'd like

These improvements to the documentation being made.

Describe alternatives you've considered

N/A