Add parallelisation config, fix --cm and add --loadSchema flag

Purpose of this PR

We enable a few new functionalities:

parallelisation can now be set in globalConfig{ parallelisation: 64; }. Recommend using 8 or 12 times the number of CPUs on the TypeDB server
excluding the --cleanMigration flag is now respected, was ignored by mistake before
--loadSchema can be passed, when not using --cleanMigration, which means schema will be loaded, as well as the data files provided
refactor the entry point of LoadOptions and TypeDBLoader