Support filtering :id type fields

[matsu911]

This change supports filtering for id type fields such as belongs_to.

[cpjolicoeur]

@matsu911 Thanks for this pull request submission.

Will you please provide a little more information on why this change is happening and what the use cases are? Is the use case simply to allow the default filters to allow filtering on model reference/relationship fields?

Also, if we do make this addition, we will need some test cases added to this pull request to support it. Currently, your changes here are failing the current test suite, and we'd need to ensure the existing tests pass, and add any new tests needed for the code changes.

[cpjolicoeur]

As a side note, you also can customize the filter config on your own by defining your own filter_config/1 function in the module that you use Torch.Pagination inside of. This way you can add or customize which filters you like for your specific use case.

[matsu911]

I attempted to use filter_assoc_select to filter by a related object, but I encountered an error stating that the corresponding _equals filter was not defined. I resolved this issue by overwriting filter_config/1 to define the filter. However, it seems that this type of filtering is a commonly encountered scenario. Therefore, it would be beneficial for Torch users if Torch allowed the default filtering by id.

[cpjolicoeur]

@matsu911 I've made a few tweaks and additions to your code and created a new PR #430 and am closing this PR as a result. Your commit authorship still remains in the new PR #430.

[cpjolicoeur]

@matsu911 Torch version 5.1.2 has been released that includes your changes here. Thanks for the pull request and work on this.