Farm names should be case-insensitive unique names on chain

[sameh-farouk]

Describe the bug

see: threefoldtech/zos_sdk_ts#1790

Currently we allow same farm name but in a different case to be inserted

https://github.com/threefoldtech/tfchain/blob/36c891c02a1758a6bd6769357fdef230886940ff/substrate-node/pallets/pallet-tfgrid/src/farm.rs#L31-L34

https://github.com/threefoldtech/tfchain/blob/36c891c02a1758a6bd6769357fdef230886940ff/substrate-node/pallets/pallet-tfgrid/src/farm.rs#L55