Add a full-sync benchmark

[drahnr]

As part of #1636 the SynState endpoint was removed, which implies removing the benchmark for it as well, however testing the new endpoint in isolation is not enough to benchmark what the user experiences in a full sync.

[Mirko-von-Leipzig]

Do we think there is a reasonable way of achieving this without using the client directly? I suspect it will be difficult to "simulate" the average user without it?