service: only initialize telemetry once to prevent errors in multiple instances

[kirbyquerby]

Description: only initialize internal telemetry once.
This change updates the init() method for colTelemetry (which is a singleton) to run at most once. This allows multiple collector instances to be run in the same process.
Link to tracking Issue: open-telemetry/prometheus-interoperability-spec/issues/34

Testing: Manually tested and was able to create multiple collectors in the same process, while previously, it would error out with:

Error: failed to initialize telemetry: processor/batch/batch_send_size: cannot register view "processor/batch/batch_send_size"; a different view with the same name is already registered                        
processor/batch/batch_send_size_bytes: cannot register view "processor/batch/batch_send_size_bytes"; a different view with the same name is already registered                                                   
kafka_receiver_current_offset: cannot register view "kafka_receiver_current_offset"; a different view with the same name is already registered                                                                   
kafka_receiver_offset_lag: cannot register view "kafka_receiver_offset_lag"; a different view with the same name is already registered  

/cc @odeke-em

[odeke-em]

LGTM, thank you @kirbyquerby!

[odeke-em]

Kindly cc-ing @bogdandrutu @alolita @Aneurysm9. This issue prevents us from creating in code multiple collectors to run the Prometheus RemoteWrite exporter tests in parallel.

[odeke-em]

Kindly help us merge this change @bogdandrutu @tigrannajaryan @alolita, before things get stale again, it is also a blocker for our work and progress