OpenTelemetry tracing manual instrumentation support

[filipecosta90]

In the same way as seen on the OpenTelemetry instrumentation forgo-redis it would be extremely beneficial to create a similar package for redigo. Not only we can track the overhead of the client code, but we can also precisely trace errors/latency spikes/timeouts/etc...

Some further info:

• Small example of goredis manual instrumentation
• Full example of HTTP service + Redis backed (with client instrumentation)

Important Note: Semantic conventions to follow while preparing a package for manual instrumentation.

While this is not mandatory, we should aim for standardization across clients/languages/DBs. Here's the spec on DB semantic conventions:

https://github.com/open-telemetry/semantic-conventions/blob/main/docs/database/redis.md

PS: will gladly contribute to this matter.

[stevenh]

This should be totally possible within an external package.

[stevenh]

Related to #642

[stevenh]

This is related to a similar conversation about adding slog support, which has me thinking about a #656 (comment) which should consider this use case as well.

Would like to hear peoples thoughts on that as an approach?