Return optional error from ApplyArgsManOptions

Also pass in a (for now unused) reference to the params.

Both changes are needed for the next commit.

ci/test/06_script_b.sh

@@ -44,6 +44,7 @@ if [ "${RUN_TIDY}" = "true" ]; then
           " src/dbwrapper.cpp"\
           " src/init"\
           " src/kernel"\
+          " src/mempool_args.cpp"\
           " src/node/chainstate.cpp"\
           " src/policy/feerate.cpp"\
           " src/policy/packages.cpp"\