Create EpochProofQuotePool

[just-mitch]

Nodes should have a new "pool" to store EpochProofQuotes, in the way there is a transaction pool, and an attestation pool.

This will provide an in memory-implementation.

Its initial interface will be:

interface EpochProofQuotePool {
  addQuote(quote: EpochProofQuote): void;
  getQuotes(epoch: number): EpochProofQuote[] | undefined;
}

[just-mitch]

Fixed in #8832