feat: add opentelemetry usage example

[daviderli614]

What's changed and what's your intention?

When after #39 merge, we can provide some example to user.

Checklist

• I have added the necessary unit tests and integration tests.

Refer to a related PR or issue link (optional)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.24%. Comparing base (d3f1530) to head (1399b2d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #47   +/-   ##
=======================================
  Coverage   74.24%   74.24%           
=======================================
  Files           7        7           
  Lines         466      466           
=======================================
  Hits          346      346           
  Misses         97       97           
  Partials       23       23           

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[sunng87]

by the way, is there any concept like feature gate or optional dependency in go? I would suggest to make otel deps optional so we keep the core sdk compact.

[daviderli614]

by the way, is there any concept like feature gate or optional dependency in go? I would suggest to make otel deps optional so we keep the core sdk compact.

Yes, a switch option has been added to the configuration. The default value is false, which means it is closed. If the user needs to turn it on, it can be set to true. Here users need to install tracing and metrics backends such as jaeger and prometheus.

cfg := greptime.NewConfig(host).WithDatabase(database).
  WithTraceProvider(tracerProvider).WithTracesEnabled(true).
  WithMeterProvider(meterProvider).WithMetricsEnabled(true)

Also, the deps go.mod is set here so as not to affect the project's main go.mod and not to pollute the contents of the main go.mod.

[daviderli614]

Modify are complete and ready for review @zyy17