Omni-Node renamings (#5915)

- moved the omni-node lib from
  `cumulus/polkadot-parachain/polkadot-parachain-lib` to
  `cumulus/polkadot-omni-node/lib`
- renamed `polkadot-parachain-lib` to `polkadot-omni-node-lib`
- added `polkadot-omni-node` binary

Related to https://github.com/paritytech/polkadot-sdk/issues/5566