Improve CID validation in Rust

[siman]

Don't check for CID length, use cid lib:

https://github.com/multiformats/rust-cid#usage

use cid::Cid;
use std::convert::TryFrom;

let out = Cid::try_from(data).unwrap();

• Update in pre-2
• Update in rc4

[F3Joule]

Since rust-cid has no no_std support, there was suggested to custom verify CID's.
For CIDv0 verify length and .starts_with("Qm").
For CIDv1 extend with:

• decode the hash to sha
• check to see if it's a valid SHA-256

[F3Joule]

Check out deeper Substrate IPFS integration.
Useful link: Substrate-IPFS Tutorial