feat: add new staking pallet

[lrazovic]

Add a new pallet to handle the parachain staking. It's a fork from Moonbeam, but without any Moonbeam specific dependency.

TODO:

• Write documentation, how to use it and what we changed from the original version.
• In a later PR: Add the Pallet to the runtime AND
• Remove the KILT's staking pallet.

[linear]

PLMC-131 Add new parachain-staking pallet to the Runtime

• Pallet: https://github.com/PureStake/moonbeam/tree/master/pallets/parachain-staking
• Runtime: https://github.com/PureStake/moonbeam/blob/51818a8d9e0ac5d0d4118c217ac7d4d4c073f4ac/runtime/moonbeam/src/lib.rs#L1326

[lrazovic]

Superseded by #48