[RSDK 4187] Custom Base Example

[ghost]

This PR adds a custom base model within the 'examples' subdirectory as a guide/template for users to follow. The new additions are loosely based on the file 'my_base.py' found at the bottom of this webpage, and also the parallel example in the Go SDK here.

This is a draft for now due to a local bug that I've been unable to fix.. stay tuned!

[ghost]

@njooma @cheukt pulling this out of draft status! Everything was locally tested using a local viam-server instance and the script found in viam-python-sdk/examples/complex_modules/client.py.

[cheukt]

LGTM

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