fix!: add a varint 0 for http to match go-libipni

[hannahhoward]

Getting an error still decoding HTTP advertisements in go. Looks like it's due to the fact that HTTP encodes a varint(0) for the payload size -- see ipni/go-libipni#22 (comment)

Tagging @willscott and @masih for visibility. I wonder if there is a way we can generate a valid ad and verify against it.

[olizilla]

I've been verifying that the ads generated by this lib are valid as far as go-libipni Advertisement.Validate() and Advertisement.VerifySignature() currently check using https://github.com/web3-storage/ipni/tree/main/scripts/verify

[olizilla]

Deployed to staging, extended provider advert created, and ingested successfully by a local instance of storetheindex

❯ ./storetheindex admin sync -p Qmc5vg9zuLYvDR1wtYHCaxjBHenfCNautRwCjG3n5v5fbs --addr "/dns4/staging-ep-ipfs-advertisement.s3.us-west-2.amazonaws.com/tcp/443/https/p2p/Qmc5vg9zuLYvDR1wtYHCaxjBHenfCNautRwCjG3n5v5fbs"

❯ curl http://localhost:3000/providers/Qmc5vg9zuLYvDR1wtYHCaxjBHenfCNautRwCjG3n5v5fbs -Ss | jq
{
  "AddrInfo": {
    "ID": "Qmc5vg9zuLYvDR1wtYHCaxjBHenfCNautRwCjG3n5v5fbs",
    "Addrs": [
      "/dns4/elastic-staging.dag.house/tcp/443/wss"
    ]
  },
  "LastAdvertisement": {
    "/": "baguqeeraxt5ikgt2oy6q4mj7tgpk6itqqpvlfoxxgh7ne52nosaggdnyhn2a"
  },
  "LastAdvertisementTime": "2023-05-22T21:18:52+01:00",
  "Publisher": {
    "ID": "Qmc5vg9zuLYvDR1wtYHCaxjBHenfCNautRwCjG3n5v5fbs",
    "Addrs": [
      "/dns4/staging-ep-ipfs-advertisement.s3.us-west-2.amazonaws.com/tcp/443/https"
    ]
  },
  "IndexCount": 12,
  "ExtendedProviders": {
    "Providers": [
      {
        "ID": "Qmc5vg9zuLYvDR1wtYHCaxjBHenfCNautRwCjG3n5v5fbs",
        "Addrs": [
          "/dns4/elastic-staging.dag.house/tcp/443/wss"
        ]
      },
      {
        "ID": "QmX5D2SHKfJEjMfUwKAJZtgXhFzmYvA66Hcc9L3ExuVDXs",
        "Addrs": [
          "/dns4/freeway-staging.dag.haus/tcp/443/https"
        ]
      }
    ],
    "Metadatas": [
      "gBI=",
      "oBIA"
    ]
  },
  "FrozenAt": null
}

base64 encoded metadata for http provider now "oBIA"`