reference: add error codes (#1816)
reference: add error codes (#1816)

* reference: add error codes

WIP

* Update error-codes.md

* Update error-codes.md

* Update error-codes.md

* reference: revise terms

* reference: update minor change in error-codes

* reference: minor change in error-codes

* change choice of words

Co-Authored-By: Jack Yu <8f822e4841d217bd92d1f6a83e7955e5f5c57cad@pingcap.com>

* Apply suggestions from code review

Co-Authored-By: Lilian Lee <c684465c17314189c18707959627e2ec4fdec2d0@pingcap.com>

* Replace illegal with invalid

Co-authored-by: Jack Yu <8f822e4841d217bd92d1f6a83e7955e5f5c57cad@pingcap.com>
Co-authored-by: Lilian Lee <c684465c17314189c18707959627e2ec4fdec2d0@pingcap.com>

pingcap/docs,pingcap/docs,pingcap/docs