[cmd/telemetrygen] Add exemplars support for telemetrygen

[jpkrohling]

This PR adds support for passing a traceID and spanID to be used as exemplars on the generated data points. This was verified with an e2e test using OTel Collector and the debug exporter in detailed verbosity, resulting in this:

2024-05-31T11:41:51.378+0200    info    ResourceMetrics #0
Resource SchemaURL: https://opentelemetry.io/schemas/1.13.0
ScopeMetrics #0
ScopeMetrics SchemaURL: 
InstrumentationScope  
Metric #0
Descriptor:
     -> Name: gen
     -> Description: 
     -> Unit: 
     -> DataType: Gauge
NumberDataPoints #0
StartTimestamp: 1970-01-01 00:00:00 +0000 UTC
Timestamp: 2024-05-31 09:41:51.374564535 +0000 UTC
Value: 0
Exemplars:
Exemplar #0
     -> Trace ID: ae87dadd90e9935a4bc9660628efd569
     -> Span ID: 5828fa4960140870
     -> Timestamp: 2024-05-31 09:41:51.374432029 +0000 UTC
     -> Value: 1

Given that I needed to do the validation of the traceID/spanID on the metrics config as well, I refactored the current validation done in the logging part of the command so that it's now part of the common package.

Signed-off-by: Juraci Paixão Kröhling juraci@kroehling.de

[codeboten]

is there a valid case for supporting only one of trace or span ID? I guess it could be used for edge case testing?

[jpkrohling]

The idea is indeed to allow for different test scenarios, like how a backend would behave in face of bad instrumentation.