log: Add global LoggerProvider

[pellared]

Problem Statement

From https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/bridge-api.md#loggerprovider

Normally, the LoggerProvider is expected to be accessed from a central place. Thus, the API SHOULD provide a way to set/register and access a global default LoggerProvider.

Proposed Solution

Add GetLoggerProvider and SetLoggerProvider to go.opentelemetry.io/otel.

Notice that this can be released only when Bridge API gets stable as go.opentelemetry.io/otel is already stable.

[MrAlias]

We cannot add support for this to otel until log is stable. If we want to support this prior to 1.0 a similar approach to https://pkg.go.dev/go.opentelemetry.io/otel/metric/global should be used.

[pellared]

If we want to support this prior to 1.0 a similar approach to https://pkg.go.dev/go.opentelemetry.io/otel/metric/global should be used.

Do you think that it is worth doing it prior 1.0? It may be inconvenient as otherwise we will make a breaking change when going stable. I would rather add it even in "1.1" as this is not a MUST in the specification and adding after the API is already stable would be more gentle for the users. This change would not affect the SDK.

[MrAlias]

I'm fine with a post-1.0. I think the metric one was motivated by a user ask and our desire to build a proof-of-concept for how it would work. I don't know of any user ask for this, currently, and I think the global implementation will be one of the easier ones.

[Kimbohlovette]

@pellared could you please assign this task to me?
@jpkrohling could I peak this one? It directly related to the project "Implement one Logging bridge" in outreachy-otel

[pellared]

It is blocked until Go Logs SDK is stable.

[Kimbohlovette]

@pellared alright thanks