Allow config.paginate to be a block

[allomov]

Hello, everyone!

I propose this change to allow config.paginate option to be set as a block that will return a value based on resource configuration.

In my case, I have a Sessions resource with an index that can be displayed as a table (default view) and as a calendar. With the calendar view, the pagination is replaced by the start/end time filter.

Using this change I can initialize resources in the following way:

ActiveAdmin.register Session, as: "All Sessions" do
  config.paginate = proc { params[:as] != "calendar" }
  index(as: :calendar)
end

which will allow ActiveAdmin::Views::IndexAsCalendar will handle filtering instead of pagination.

Thank you for your attention! Please, tell me what you think about it.

[allomov]

I am not sure why CI is failing, because the same command for test (3.2, rails_70) and other configurations work fine, but fail on test (3.2, rails_61)

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.26 🎉

Comparison is base (15800ce) 98.84% compared to head (b037309) 99.11%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8007      +/-   ##
==========================================
+ Coverage   98.84%   99.11%   +0.26%     
==========================================
  Files         197      197              
  Lines        4950     4949       -1     
==========================================
+ Hits         4893     4905      +12     
+ Misses         57       44      -13     

Impacted Files	Coverage Δ
lib/active_admin/resource/pagination.rb	100.00% <100.00%> (ø)
...ib/active_admin/resource_controller/data_access.rb	100.00% <100.00%> (ø)

... and 6 files with indirect coverage changes

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