Enable customization of default dimensions and properties

[Dunedan]

Log records by default already contain several dimensions ("LogGroup", "ServiceName"and "ServiceType") and properties (in case of the AWS Lambda environment "executionEnvironment", "memorySize", "functionVersion", "logStreamId" and "traceId"). While I believe that these dimensions and properties are great defaults, they make resulting log records already pretty large. Especially for applications which log many metrics, resulting in a huge number of log records, that might result in higher than necessary cost for CloudWatch Logs, if these dimensions and properties aren't valued.

While it's currently possible to use MetricsLogger().set_dimensions() to remove the default dimensions on a per-scope basis, I haven't found a similar way for properties. Also the need to replace the defaults per metrics scope is pretty repetitive, so I'd prefer a global option to customize the default dimensions and properties instead.