Find fingerprints using only partial digest

[joshpencheon]

The digests used as error fingerprints are pseudo-random, so it would be reasonable to accept "short" versions of them in URLs (with a check to ensure they're not ambiguous).

So:

https://my-app.com/fingerprinting/errors/625d8e27fe0f60e50865e6e11273aee437d9c5e7

could be accessible as

https://my-app.com/fingerprinting/errors/625d8e27

but probably not

https://my-app.com/fingerprinting/errors/6