Support for explicit party specifications on Streaming WS endpoints

[ray-roestenburg-da]

Split from https://github.com/digital-asset/daml/issues/11200, which was closed by https://github.com/digital-asset/daml/pull/11454 except for support for the streaming endpoints, which is the remaining work captured in this ticket.

From the original ticket:

Currently, the JSON API does not support specifying parties explicitly for streaming endpoints. Instead it always infers them from the token.

This is convenient in a lot of circumstances but it causes issues in others. E.g., for Daml script if you have a token with actAs = [Alice], readAs = [Public] you always need to use submitMulti [Alice] [Public] because Daml Script cannot restrict the claims available for a submission to a subset of the token.

Adding optional parameters to the JSON API to specify actAs and readAs would solve this nicely while keeping the convenience.

This comment asks the questions how particular endpoints should implement specifying parties explicitly. This response shows no preference for streaming endpoints for this to be specified per query or in a messages preceding the queries, which is the remaining question to be answered in this ticket.