pinning service API needs to reject IPLD codecs we don’t support

[heyjay44]

• pinning service API needs to reject IPLD codecs we don’t support (for both web3.storage and NFT.Storage)
• document that we support remote pinning the following codecs raw dag-json dag-cbor dag-pb in the root node and outside of that, we’ll reject (here https://web3.storage/docs/how-tos/pinning-services-api/ and https://nft.storage/docs/how-to/pinning-service/)
• also add to the API reference docs of each
• easiest way we can get this enforced in the API for now is to return non-200 responses to the pinning service API (decode the cid in full, get its codec, compare, reject)

[flea89]

Doc updates are tackled in a separate PR