Using a label named "endpoint" is not intuitive and requires explaining to
users that it's really just the Cluster::node value. Change the label to
"node", so that we don't need to do the explaining.
This probably breaks some existing users of the Prometheus metrics, but after
looking more at metrics recently, "endpoint" really is a thorn in my eye.
This moves the Telemetry framework's BIF-defined functionalit from the
secondary-BIFs stage to the primary one. That is, this functionality is now
available from the end of init-bare.zeek, not only after the end of
init-frameworks-and-bifs.zeek.
This allows us to use script-layer telemetry in our Zeek's own code that get
pulled in during init-frameworks-and-bifs.
This change splits up the BIF features into functions, constants, and types,
because that's the granularity most workable in Func.cc and NetVar. It also now
defines the Telemetry::MetricsType enum once, not redundantly in BIFs and script
layer.
Due to subtle load ordering issues between the telemetry and cluster frameworks
this pushes the redef stage of Telemetry::metrics_port and address into
base/frameworks/telemetry/options.zeek, which is loaded sufficiently late in
init-frameworks-and-bifs.zeek to sidestep those issues. (When not doing this,
the effect is that the redef in telemetry/main.zeek doesn't yet find the
cluster-provided values, and Zeek does not end up listening on these ports.)
The need to add basic Zeek headers in script_opt/ZAM/ZBody.cc as a side-effect
of this is curious, but looks harmless.
Also includes baseline updates for the usual btests and adds a few doc strings.
