[Whitelisted Caller] Increase max_validators to 600

This referenda increases the parachain validator set size from 600 to 700.
The maximum backing group size is kept to 5, so the total number of usable cores increases to 140.

Additionally, also update the setNDelayTranches from 257 to 299, so that the number of assignments per candidate stays constant to around ~2.33, the justification why this is the desired value for this parameter can be found in ELVES https://eprint.iacr.org/2024/961 paper and here.https://github.com/paritytech/polkadot-sdk/issues/6853#issuecomment-2540373492.