Allow setting up global attributes for all signals

[LikeTheSalad]

The current global attributes appender is targeted to Spans only (most likely due to historical reasons), this can cause issues such as some signals not having key dynamic attributes such as the session id for example, as mentioned in this comment.

Because of the above, we need to come up with a way to provide global attributes not only to all Spans but also to Metrics and Logs.

[LikeTheSalad]

This has been done for logs already and I don't think we'll need it for metrics. So closing for now.