Initial DA API Spec structure

[bacv]

The idea is to compose 3 entities (Sender, Receiver, Producer) using DA executable spec components and spawn them in tests.

• Zone - EZ/Client that 1) creates data; 2) disperses it; 3) sends to Producer.
• Node - DA Node that receives chunks from Senders.
• Producer - Block Producer that receives Certificates with Metadata from Senders.