Add Suborigin, Etag and X-Ipfs-Path headers

[lidel]

I feel we should aim at header-parity with go-ipfs.

To future-proof it, it should be CIDv1 in Base32 everywhere:

$ curl -I https://ipfs.io/ipfs/bafkreigh2akiscaildcqabsyg3dfr6chu3fgpregiymsck7e7aqa4s52zy
...
Etag: "bafkreigh2akiscaildcqabsyg3dfr6chu3fgpregiymsck7e7aqa4s52zy"
X-Ipfs-Path: /ipfs/bafkreigh2akiscaildcqabsyg3dfr6chu3fgpregiymsck7e7aqa4s52zy
Suborigin: ipfs000bafkreigh2akiscaildcqabsyg3dfr6chu3fgpregiymsck7e7aqa4s52zy

Notes regarding Suborigin:

• Suborigin header must be lowercase kubo#3209 (comment)
• Suborigins  in-web-browsers#66 (comment)

Additionally, resources from /ipfs/ namespace should be returned with immutable flag:

• Cache-Control: public, max-age=29030400, immutable