Allow BigInt size of autoincrement idField type

[MurzNN]

At now autoincrement idField type have only Int format, but it is not enough for large amount of data. Please add support for BigInt database field format to extend limitation of max stored items number.

As alternative we can use cuid or uuid kind, but performance of that identifier types are several times worse, than with numeric ids, that especially signally in tables with many rows!

So BigInt storage format is the most optimal way!

[MurzNN]

Here https://github.com/MurzNN/keystone/commits/idfield-overrides-2 is my patch that implements BigInt id field type, using idField override custom feature.

[MurzNN]

And here #7188 is my attempt to implement this feature.