Add tracing support

[augustuswm]

Really liked using looker with nexus logs and wanted to use it on json formatted tracing logs.

• Add support for different source entry types
• Add support for reading and emitting tracing logs

[jclulow]

What does it look like visually when you push some tracing entries through it?

[augustuswm]

I tried to keep it close to the way the Bunyan logs look. Notably we do not have a dedicated host field, and can have an array of spans associated with a record.

(records without spans)

22:24:57.156Z DEBG cassette_sync::sf::jobs::check_for_completed: Completed job
    job = check_for_completed
22:24:57.629Z DEBG cassette_sync::sf::jobs::reserve_pending_requests: Completed job
    job = reserve_pending_requests

(records with spans)

2023-11-03 14:25:29.887Z DEBG rfd_processor::github: Ignoring branch for RFD number that is in a final state on the default branch
    number = 13
    span[0] = Process branch
    span[0]::branch = "0013"
    span[0]::commit = "13bd24ff1c4998da7203db502501bd64fdd9142d"

Just noticed though that the span version is missing the span name. I'll need to add that.

Or as an alternate display:

2023-11-03 14:25:29.887Z DEBG rfd_processor::github: Ignoring branch for RFD number that is in a final state on the default branch
    number = 13
    span[0] = Process branch
        branch = "0013"
        commit = "13bd24ff1c4998da7203db502501bd64fdd9142d"

Not sure which is preferable. Ended up switching to the tab display to reduce some of the repeated noise.