ex fb ads: support ad_id in primary key

[kacurez]

If query path(aka endpoint) is empty and there is ad_id in the columns then ad_id will be also contained in the primary key of the resulting table. It is needed for queries such as:

path: "" (empty string)
fields:

insights.time_range({"since":"2019-09-01","until":"2019-09-30"}).level(ad).time_increment(1){account_id,account_name, ad_name, ad_id,impressions,clicks,spend}

detais here https://keboola.slack.com/archives/C1B7SH7T2/p1569917984001200

[pivnicek]

Lisp blows my mind, but I get what's going on I think:)

lgtm

[kacurez]

Yes your are right about the ad_id is only add to PK if the path is root. I will merge after I notify owners of those couple of configs that will be affected. thanks!