Linq: added CountAsync() helper on FdbRangeQuery

- Can be used later to add an optimized path when counting ranges (no need to accumulate all the keys/values in memory)
Logging Filter: added SetOption command to be able to log options being set on transactions
Made some change to speed up Fdb.System.EstimateCountAsync:

- disable ReadYourWrites on the transaction to reduce the amount of data read from the db (at the custom of some added latency)
- switch to using get_range when the windows size is small enough.
- cleaned up debug traces