Pruning to conver to Half-path

[xanatos]

One of the ways to convert to the Half-path db format is to do a full pruning while having the --Init.StateDbKeyScheme HalfPath parameter. I think in the log the fact that there will be a conversion of the db format should be written. I had to relaunch the Nethermind to be sure that the conversion had happened (when launching Nethermind, if the db is in Half-path format, in the log it is written Detected HalfPath key scheme).