Add New Networks

Linea, Linea Testnet and Holesky.

Linea: New ZK-EVM from Consensys. Seems to be well used, should be legit by definition.
Holesky: Successor to Sepolia, will replace Sepolia - support is mandatory.

All endpoints are standard Etherscan, so can be dropped in without any work.

Disclaimer: It's not urgent, but something we should add because Holesky is definitely going to be needed and it's good to support a zkevm chain. The Holesky logo is a placeholder, there's currently no official logo. Feel free to not use it.

Linea:
ID: 59144
RPC: ```https://linea-mainnet.infura.io/v3/xxxxxx```
Etherscan TX: ```https://lineascan.build/tx/```
Etherscan API: ```https://api.lineascan.build/api?```
Symbol: ETH

CoinGecko ID for Linea: ```linea``` (for both ERC20 token and chain price lookup). However, Linea is an L2 pegged against Ethereum price same as Optimism etc. Invoking 'linea' on Coingecko to look up the price will return 'not found'.

Linea Testnet:
ID: 59140
RPC: ```https://linea-goerli.infura.io/v3/xxxxxx```
Etherscan TX: ```https://goerli.lineascan.build/tx/```
Etherscan API: ```https://api-testnet.lineascan.build/api?```
Symbol: ETH

Holesky:
ID: 17000
RPC: ```https://rpc.holesky.ethpandaops.io```
Etherscan TX: ```https://holesky.etherscan.io/tx/```
Etherscan API: ```https://api-holesky.etherscan.io/api?```
Holesky symbol: HolETH