Added ActiveRecord::Base#has_secure_key (via ActiveRecord::Securekey)

This is how the API will look like.

- [X] Done Implementation. 
- [ ] Documentation's work is in progress

fixes #16879 
cc @dhh 
If you would create `"set_generated_#{ attribute }_key"` outside of `define_method` block and use in block as local variable it will probably increase performance because this string will not need to be generated on call.