samples: add 'rpc' testing and convert 'logging' to Golioth Python lib

[mniestroj]

Add Golioth Python package that contains library with simple CLI tool to access Golioth services and communicate with device (indirectly via cloud).

Add basic pytest runtime test for rpc samples, which tries to call RPC method multiply several times and verify returned results.

Convert also samples/logging/ pytest script to use introduced Python package, instead of calling goliothctl subprocess. This shows clearly what are the differences of both solutions in test case implementation.

[github-actions[bot]]

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