feat: Add Environment & Services support

[JamieDanielson]

Which problem is this PR solving?

• closes #308

Short description of the changes

If using an environment-aware key:

• dataset = serviceName
• add field of service.name in addition to service_name to be more consistent with otel
• use default service name of unknown_service:<processname> or unknown_service:go if process name is unavailable and no service name provided
• don't propagate dataset by default unless legacy key (to prevent overwriting of service name)
• warn on missing service name and api key
• warn on presence of dataset, noting data will be sent to service name
• if dataset derived from service name starts with unknown_service*, truncate to unknown_service for dataset
• if dataset derived from service name has extra whitespace, trim whitespace and console warn on diff

warning provided if dataset is set in config when using environment key: WARN: Dataset is ignored in favor of service name. Data will be sent to service name: message-go warning provided if extra whitespace detected in service name: WARN: Service name has unexpected spaces

If using a classic key:

• dataset is dataset in config, with default of "beeline-go"
• add field of service.name in addition to service_name to be more consistent with otel
• use default service name of unknown_service:<processname> or unknown_service:go if process name is unavailable and no service name provided
• dataset propagates by default
• warn on missing service name, api key, dataset

warnings provided if no env vars set and using classic key:

WARN: Missing dataset. Data will be sent to:beeline-go WARN: Missing API Key. WARN: Missing service name.