De-couple starting a trace server with opening a trace.

We currently cannot start a trace server without opening a trace. My understanding is that we want to search available `TraceServerContributor`s for one where the trace being attempted to open is already available.

It would be simpler to have the functionality of opening a trace and starting a trace-server de-coupled. The functionality of starting a trace-server without the need of a file path would be invaluble.

## My understanding and suggested solution:

Instead of having one current route for starting a server:
1) Start Trace Server with mandatory file path

We could have three options:
1) Start Trace Server with optional file path, searching available `TraceServerContributor`s for one with the trace open (previous implementation).
2) Start ANY trace server from ANY `TraceServerContributor` (if any)
3) Open a trace with a current and available `TraceServerContributor`.