expose module errors into metadata (#3752)

* expose module errors into metadata

* it checks

* Tests for error metadata

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <[email protected]>

* remove inherent errors from metadata

* bump version

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <[email protected]>

* Update srml/support/src/error.rs

Co-Authored-By: Bastian Köcher <[email protected]>