Fix schemas that don't handle to_string function data

Validation done by the row-schema for fact-contents endpoint
(https://github.com/puppetlabs/puppetdb/blob/6.x/src/puppetlabs/puppetdb/query/fact_contents.clj#L10-L24)

fails for rows on which we apply the to_string function.
We also need to make sure that there are no other schemas that might throw errors because of this.

This can be reproduced with this query:

["extract", [["function", "to_string", "value", "9999999"]], ["=","name", "uptime_seconds"]]

on the facts endpoint.

If you add a formatting mask, like "9,999", the query won't fail, but no result is given. Do we need a default formatting mask for integers?

There is a disabled unit test with this ticket id. It has to be enabled once this is fixed.