[Whitelisted Caller] Referendum #219: Increase Parachain Validators to 300

The proposal follows good network stability with 250 parachain validators (as set in Referendum 188), and aims to further increase the number of validators participating in parachain validation from 250 to 300. Please note that this is part of the Network scalability roadmap aiming for 500 parachain validators, and now up for vote by the community.

All info can be found on the proposal post. Note that the proposal has been submitted on Whitelisted Caller track: meaning the Fellowship is also voting on a proposal (no. 40) to whitelist the submission hash.