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
```

bash/ostree

@@ -1381,9 +1381,9 @@ _ostree_remote() {
         delete
         delete-cookie
         gpg-import
+        gpg-list-keys
         list
         list-cookies
-        list-gpg-keys
         refs
         show-url
         summary