Using $facet instead of two queries & adding paginateExec to Aggregate

[claude-abounegm]

This pull request contains two features:

• $facet operator is now being used by default instead of executing two queries. To disable, pass useFacet: false to the options.
• Mongoose's Aggregate is extended and paginate can now be called directly using aggregate.paginateExec(options, [cb]).

If countQuery and useFacet, two queries will still be executed, and facet will be ignored.

Breaking Changes:

• $facet and $count require mongo 3.4+
• $facet is now used by default.

[aravindnc]

@claude-abounegm Much thanks.

[aravindnc]

@claude-abounegm Can you add a test case too.

[claude-abounegm]

@aravindnc will do soon!

[saminndex]

FYI there's a breaking change that's not mentioned which means you cannot use $geoNear queries when useFacet is set to true with the error message $geoNear is not allowed to be used within a $facet stage so if you're using this in your aggregatepaginate query using the mongoose-aggregate-paginate-v2 package, you'll need to set this to false. Further reading: https://www.mongodb.com/docs/manual/reference/operator/aggregation/facet/