Improve copyStruct() function to be case insensitive

[maksym-nazarenko]

Currently, copyStruct() func is searching fields in the target struct by the field's name.
This search is done by 1-to-1 mapping of field names, so ID != Id.

This behavior should be changed, so fields mapping is done in a better way.
Options are:

1. case-insensitive search (probably, easier in short term)
2. use struct tags for field naming (requires adding tags to all models in Terraform resources and MikroTik client packages)