pds migration does not preserve extra did document entries

extra did document entries for did:plc identities (services that are not #atproto_pds and alsoKnownAs entries which do not match the provided handle) are stripped from the did document during migratio. extra services and non at:// AKA entries should be easy enough to detect, although extra at:// entries may need some tweaks

not a huge issue as barely anyone will have extra services/akas at the minute and its fairly easy to get them back, but prolly worth sorting incase it does become an issue later down the line