[Refactor] Gas network symbol

[tiagofilipenunes]

When adding a network using wallet_addEthereumChain, MetaMask expects a gas network symbol to have a length between 2 and 6 characters.

To allow new networks to be added on CELO, which uses a symbol longer than the 6 characters, any parenthesis and content from the symbol string are removed, and its length is limited to 6 characters. This issue is to refactor this implementation and improve the way the config symbol is used to add new networks.