Use stacks block timestamp for block ingestion

[zone117x]

Stacks block timestamps have been added to Nakamoto blocks in https://github.com/stacks-network/stacks-core/pull/4846

API code currently takes Date.now() during block ingestion for this value: https://github.com/hirosystems/stacks-blockchain-api/blob/eada84e2ce7b5decf75e29809f91f33fd8e6ae21/src/event-stream/event-server.ts#L251-L258

• Needs to be adjusted to use the value from the core node event
• Core node /new_block event may need modified to include this new value

[zone117x]

Confirmed this is working as expected with latest stacks-core develop 🎉