Support Count on Manual Read

[allenwyma]

Is your feature request related to a problem? Please describe. APIs sometimes contain a count, and we can wrap APIs with an Ash.Resource and use a manual read to query. As far as I know, only ash_postgres can support count when we paginate. I’d like if if on manual read we can supply our own count so we can use a more clear count.

Describe the solution you'd like As suggested by Zach, including the option of :count? that will get passed into the manual read, we can return the value of count if requested.

Describe alternatives you've considered A clear and concise description of any alternative solutions or features you've considered.