Fix base-path handling in `key insert` (#7775)

This fixes the handling of base-path when using `key insert`. Before
the base-path wasn't setup correctly, as done when starting a node. This
resulted in putting the keys into the wrong directory. This pr fixes
this by creating the correct base-path/config dir for the keystore.
Besides that it also removes the insert command from `subkey` as it
doesn't make that much sense. If requested, we could bring it back later.