API filtering by api_key column does not work as expected

It may be that not working is how this should behave, but reporting since the behaviour is unexpected.

If I use API to filter as eg "first_name LIKE 'a%'", I get results.

If I use API explorer similarly to query "api_key LIKE 'a%'", I get:

{
    "error_code": "not-found",
    "entity": "Contact",
    "action": "get",
    "is_error": 1,
    "error_message": "Error in call to Key_get : API (Key, get) does not exist (join the API team and implement it!)"
}

IMO we probably don't want people to be able to query API keys via API anyway (until there are permissions around that sort of usage) so we should special case this.