Logging/Tracing Support

[theduke]

This issue aims to discuss the design of logging and tracing support in Juniper.

Requirements:

• Minimal performance impact (potentially completely disabled with a feature)
• Backend-independet, so users can utilize log/tracing data the way they want to
• offer fine-grained (request + resolver based) tracing information
• have a good out-of-the-box experience (ideas? slow resolver warnings, ...)

Crates to consider:

• tracing
• tracing_log