feat (cedarling): Log Startup message

[nynymike]

After init is called, the cedarling should write a startup log message with details about its configuration. This is a good way to test the log functionality via Python too.

Identified code changes

• Create new log interface in Rust
• Add CEDARLING_LOG_TYPE bootstrap variable to control logging behavior, default to in_memory
• Add CEDARLING_LOG_EXP_TIME bootstrap variable, default to 60
• Create log message in cedarling memory and expire it accordingly
• Adjust Python binding for response, which should be a dictionary of log messages, each with a unique identifier representing the log message identifier, so the client can discard duplicate messages if they happen to return.

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Test cases and code coverage

• Rust unit test
• Python integration test

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Document the changes

• Update python docs
• Make sure method in Rust is propery documented with an example.

[olehbozhok]

we discussed that it would be OK to use Circular buffer so I change CEDARLING_LOG_EXP_TIME to the CEDARLING_LOG_CACHE_SIZE

[nynymike]

Ok for now.