[v2] Access/Audit Logging from network observer

[c-kruse]

In v1, the flow-collector logs an event when the collector first adds a vanflow record and again when the collector deletes that record. This compromise kept log noise low enough for the always-on nature of the collector logging, and managed to expose enough information for 1. developers and operators to attempt to debug collector and network issues and 2. to serve as a plausible audit trail answering the question "which service was a skupper network connection or request routed to?".

Moving forward, we should consider a dedicated facility for the later case, in the form of a configurable "network access logging" option to the network-observer.

• Should be configurable (method and granularity TBD)
• Should emit predictable structured events, with the fullest amount of relevant context known (source and dest host, process, site, proxy host, router trace path, etc.)
• [non functional] Appears familiar to end users who understand traditional network and application load balancer access logs, but are not "skupper nerds."

[c-kruse]

@Karen-Schoener this one made me think of you all with the work you've been doing on flow metrics. Would be curious to hear your thoughts sometime. I suspect our horizon for this would be post-2.0, so no rush!