[FEATURE-REQUEST] Allow searching by id

[tensiondriven]

Describe the problem you're proposing to solve

A common use case for an admin panel is to look up a record by id. I can add :id by implementing search_fields(), but according to https://github.com/aesmail/kaffy#search only string fields are supported.

Describe the solution you'd like
Support searching on numeric fields in addition to :string / :text.

Describe alternatives you've considered

Typing the id into the URL (assuming the resource id is the id i want)

Additional context

This is a brilliant piece of work and much needed in the Elixir/Phoenix community... and finally done right. Already useful, and, can't wait till its more fleshed out.

[aesmail]

I actually needed this today, a lot. It's safe to assume this is coming in the next minor release.