Add a --check-config option for cli commands

this allows to specify on command line wether to check the configuration
and read or write access to the storage at startup time (especially for
rpc-server and replay commands.)

Warning: this option defaults to "read" for the backfill command and
"write" for rpc-serve and replay commands, so now the creation of
the Storage instance used in cli commands *will be checked*.

Closes T2525.