Pair and unpair for both sharer and helper

[lbaird]

In DeRecMessage, the pair and unpair requests and bodies are listed under sharer. They should be listed under both sharer and helper, since either could send them. So those 4 fields should be added to the helper.

[jorabin]

Noting that there is a wider review of authentication context and secrets that may change the perspective on this.

There's nothing preventing access to the protobuf binding api whether or not you're an actual helper or sharer, but understood that it's incorrect as a piece of documentation.

Wondering if we should just remove the categorisation as it makes the apis slightly harder to use.