Adding a new method to action classes to return permitted param declarations

[jwoertink]

Purpose

This is a precursor to #1070

Description

Before this PR there was no way to know what params have been defined on an Action class. Also interesting thing, calling something like Users::Index::PARAM_DECLARATIONS would throw an exception that Crystal::Macros::TypeDeclaration was undefined. I guess that constant only lives inside of macros...

Well, now we have a method called permitted_query_params on the class. This will be useful for adding which params are allowed in a route when running lucky routes.

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test

[paulcsmith]

Looks good. Just one comment on a name for it