refactor: iroh-share uses iroh-embed

[ramfox]

iroh-share currently imports the p2p and store directly, it should instead but using iroh-embed to spin itself up.

We also need to add gossipsub to the API, for use in iroh-share

• feat(rpc, api): add network_events, and Gossipsub IPC methods #16
  - way to get NetworkEvents from p2p node in P2pService
  - add gossipsub_subscribe, gossipsub_publish, etc to iroh-api
• refactor iroh-share to use iroh-embed