Add new postfix ".tknx.near" for auto-whitelisting

Similar to “.tkn.near”, now there is a new NEAR account domain, “.tknx.near” for the community to mint tokens freely.
We apply to add this new domain as postfix of auto-whitelisting in ref-exchange.

This is an extension of the auto-whitelisting efforts relating to tkn.near tokens. tknx.near tokens pertain to token addresses generated via tkn homes - Grow your own token which the Ref team manages.