[python] add socket_options to configuration for the rest client

[meadsteve]

This PR adds a property to the configuration object for the generated code rest client called socket_options. This property is passed down into urllibs3's ProxyManager/PoolManager as addition_pool_args. This extra key word argument should be picked up by the underlying HTTPConnection objects.

This enables consumers of the generated client to configuring the underlying connection if needed. In my specific use case I need this to set some keepalive settings for the connections.

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cc @spacether

[spacether]

closing and re-opening to kick off ci again

[spacether]

@meadsteve this looks great, thank you!
Would you be willing to add a test asserting that the socket options are being used by the PoolManager?
In the past we have had features break because no tests were ever written verifying that a feature existed, and someone tweaked code and broke something. Adding a test would protect this feature in the future.
A good place to put a test is this folder.

[meadsteve]

Thanks. The tests sound good but I wasn't sure where to start so thanks for the suggestion.
The build still looks like it's failing but I'm not sure it's something I've done?

[spacether]

Yup, that CI error is unrelated to your PR; please ignore it.

[meadsteve]

@spacether I've added a test to cover this in python_experimental. I couldn't see any existing structure to do this for the non experimental python. Let me know if there's anything else you'd expect to see before this gets merged.

[spacether]

This looks great!
Thank you for the PR and for adding the tests!