Make label prefixes user configurable

[tomsons26]

currently to ignore prefixes somewhat specific to my workflow i have to edit is_local_label to have
const LABEL_PREFIXES: &[&str] = &[".L", "off_", "loc_", "LAB_", "$L"];
would be good if these were specifiable in the config file instead as there's many prefixes across many compilers/assemblers, objdiff shouldn't be trying to cover them all

[ifarbod]

{
  "ignore_local_labels": [".L", "LAB_", "loc_", "jpt_", "off_", "switchD_", "$L"]
}

Something like this could work, it is preferable to be project-specific, so it'd go into objdiff.json.
switchD_ is so universal now it might as well be in the default list.