Semantic Convention for redundant connections

[sirzooro]

When system uses redundant connections, the same message is sent via multiple paths to destination. Current version of net.* attributes allows to specify single value only, so sender would have to create child span for every path in order to track all of them. I propose to extent them to allow using arrays too in addition to existing scalar string/int values. For example destination addresses could be reported as net.peer.ip = ["10.1.1.1", "10.2.2.2"].

You also could add recommendation that code should either use scalars value for all net.* attributes, or arrays with the same element count for all of them.

In my case message receiver drops duplicate messages and passes only one copy of them to upper layers, so existing set of net.* attributes are enough. However in general case it may be useful to use arrays on receiver side too.