count documents api

[abose]

There should be a way to get count of documents in store without doing a full database read. SQL count(primarykey) should do this in O(1). This should also support query format.

For Eg. Right now, there is no way to do getCount(publishedExtensions) without doing a full scan of the table.

let count = await countDocuments("tableName");
let count = await countDocuments("tableName", query, indexedFields);