Add SQL commenter as context propagation for databases

[XSAM]

Part of #2162, Replace #2236. All previous commits are copied to this PR.

This PR focused solely on the SQL commenter, as #2363 has been merged.

XSAM/otelsql#512 is the prototype that demonstrates the SQL commenter with the text attributes propagator.

Changes

Add SQL commenter as context propagation for databases

[XSAM]

@open-telemetry/semconv-db-approvers PTAL

[XSAM]

@trask, I find all comments are resolved. Is that okay for you to approve this PR?

[lmolkova]

Suggested change

	If the propagator does not provide any value, the instrumentation SHOULD NOT inject any comment into the query.
	If the propagator is not provided, the instrumentation SHOULD NOT inject any comment into the query.

?

[XSAM]

This prevents injecting empty comments like /**/ when the propagator sets nothing.

So, we won’t see a query like this SELECT * FROM Users /**/

[lmolkova]

Perhaps you meant something like this then

Suggested change

	If the propagator does not provide any value, the instrumentation SHOULD NOT inject any comment into the query.
	If the context is empty or invalid, the propagator SHOULD NOT inject any comment into the query.

?

But this sentence immediately follows "The instrumentation SHOULD allow users to pass a propagator to overwrite the global propagator.", it seems it intends to talk about propagator not being provided by the user.

[XSAM]

We can use this code as the example. In this example, even the propagator provides nothing, the comments will be injected.

https://github.com/XSAM/otelsql/blob/370716b2f8c317607879035937ba65cfc751dc5a/commenter.go#L66

return fmt.Sprintf("%s /*%s*/", query, cc.Marshal())

Since it is instrumentation's job to actually inject the comment, the instrumentation should be the one to be regulated for this, not the propagator.

[XSAM]

I updated this part on c0a6f4b. I think it is clear now.