sdk/log: Record.Resource to return *resource.Resource (#6864)

Fixes https://github.com/open-telemetry/opentelemetry-go/issues/6863

From https://pkg.go.dev/go.opentelemetry.io/otel/sdk/resource#Resource:

> Resource is an immutable object
> [...]
> Resources should be passed and stored as pointers
(`*resource.Resource`)

In all other places the exported API uses `*resource.Resource` and not
`resource.Resource`.

exporters/stdout/stdoutlog/record.go

@@ -106,7 +106,7 @@ func (e *Exporter) newRecordJSON(r sdklog.Record) recordJSON {
 
 		Attributes: make([]keyValue, 0, r.AttributesLen()),
 
-		Resource: &res,
+		Resource: res,
 		Scope:    r.InstrumentationScope(),
 
 		DroppedAttributes: r.DroppedAttributes(),