Add async benchmark for logback-logstash-encoder

[brenuart]

The logback-logstash-encoder (LLE) project comes with an AsyncDisruptorAppender wrapper that can be used to log asynchronously to an otherwise synchronous appender.

This PR adds a benchmark in the AsyncWithFileAppenderBenchmark test suite to evaluate the LLE async solution alongside the other ones.

A few points about the integration:

• Instead of creating a separate logback configuration file, I reused the existing one and added a new appender named "LLE"
• The "LLE" logger category logs to this new appender and has additivity turned off to avoid logging into the other appender as well
• The logbackLleFile benchmark logs directly to the LLE category to target the LLE appender.

Thanks for considering adding this benchmark to your suite.