chore: add opentelemetry example

[vmihailenco]

I will continue working on this, but it is a decent preview of how it will look.

[vmihailenco]

Regarding the instrumentation, I've noticed 2 things:

• db.statement attribute is missing which is rather useful to have, for example, db.statement = "set key value"
• looks like $redis->multi() and $redis->pipeline() require more work

@tillkruss I can try to address both issues, but wanted to check with you first.

[tillkruss]

Good catch, feel free to add both.

The db.statement could be extremely massive. I read somewhere that values should be omitted, just keys should be logged.

[vmihailenco]

I've sent #32 to record db.statement, but multi and pipeline look somewhat complicated so we probably should leave it for later. E.g. should we create a separate wrapper for mutli/exec? Or we can expect the state of existing Relay instance? Hard to tell without the source code...

I read somewhere that values should be omitted, just keys should be logged.

That recommendation only applies for span names. Attributes can be arbitrary large, for example, it is a common practice to record SQL queries which can be much larger than Redis commands.

[tillkruss]

but multi and pipeline look somewhat complicated so we probably should leave it for later. E.g. should we create a separate wrapper for mutli/exec? Or we can expect the state of existing Relay instance? Hard to tell without the source code...

Relay works just like PhpRedis for transactions: https://github.com/phpredis/phpredis

[tillkruss]

I've done the MULTI wrapping in Object Cache Pro, will take a look today how it could be handled.