Telemetry framework: move BIFs to the primary-bif stage

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.

(cherry picked from commit 71f7e89974)

scripts/base/init-bare.zeek

@@ -5787,15 +5787,11 @@ export {
 	const flowbuffer_contract_threshold = 2 * 1024 * 1024 &redef;
 }
 
+@load base/bif/telemetry_functions.bif
+@load base/bif/telemetry_types.bif
+
 module Telemetry;
 export {
-
-	type MetricType: enum {
-		COUNTER,
-		GAUGE,
-		HISTOGRAM,
-	};
-
 	## Type that captures options used to create metrics.
 	type MetricOpts: record {
 		## The prefix (namespace) of the metric. Zeek uses the ``zeek``