bin/remote: Rename list-gpg-keys to gpg-list-keys

As pointed out in the original review, `gpg-list-keys` fits better
alongside the existing `gpg-import`.

Changes were done with:

```
git grep -l list-gpg-keys | xargs sed -i 's/list-gpg-keys/gpg-list-keys/'
for src in $(git ls-files '*list-gpg-keys*'); do
  dst=${src/list-gpg-keys/gpg-list-keys}
  git mv "$src" "$dst"
done
```

src/ostree/ot-builtin-remote.c

@@ -44,7 +44,7 @@ static OstreeCommand remote_subcommands[] = {
   { "gpg-import", OSTREE_BUILTIN_FLAG_NONE,
     ot_remote_builtin_gpg_import,
     "Import GPG keys" },
-  { "list-gpg-keys", OSTREE_BUILTIN_FLAG_NONE,
+  { "gpg-list-keys", OSTREE_BUILTIN_FLAG_NONE,
     ot_remote_builtin_list_gpg_keys,
     "Show remote GPG keys" },
 #endif /* OSTREE_DISABLE_GPGME */