[META 896] Set User-Agent in OTLP exporters

[elastic-observability-automation]

See meta issue for the description and details:

• Meta issue: [Meta] EDOT SDKs Telemetry: Set User-Agent in OTLP exporters apm#896

Exporters to customize

• http/protobuf
• http/json
• grpc

[trentm]

see open-telemetry/opentelemetry-js#4447

[trentm]

carry over from it-109

[david-luna]

upstream issue open-telemetry/opentelemetry-js#5601

[david-luna]

OTEL spec issue: open-telemetry/opentelemetry-specification#4479

[david-luna]

blocked until the issues above are resolved

[david-luna]

this may be related open-telemetry/opentelemetry-js#5719