* Scan and list keys matching a regular expression.
*
* Arguments:
* 1. "namespace" (string) namespace Id
* 2. "initiator" (string, optional) Options are "all", "self" and "other", default is "all". "all": all the namespaces, whose participation in the group is initiated by this namespace or other namespaces. "self": only the namespace whose participation is initiated by this namespace. "other": only the namespace whose participation is initiated by other namespaces.
* 3. "regexp" (string, optional) filter keys with this regexp
* 4. "maxage" (numeric, optional, default=96000) only consider names updated in the last "maxage" blocks; 0 means all names
* 5. "from" (numeric, optional, default=0) return from this position onward; index starts at 0
* 6. "nb" (numeric, optional, default=0) return only "nb" entries; 0 means all
* 7. "stat" (string, optional) if set to the string "stat", print statistics instead of returning the names
*
* Result:
* [
* {
* "key": xxxxx, (string) the requested key
* "value": xxxxx, (string) the key's current value
* "txid": xxxxx, (string) the key's last update tx
* "height": xxxxx, (numeric) the key's last update height