Stubs for raw context calls (BCD)

[m-kus]

How to test/reproduce:

• Deploy a contract to the rollupnet (with bigmaps)
• Go to the storage -> bigmap viewer
• Currently there will be console errors due to the http 404/500

Endpoints:

• https://rollupnet.zaun.baking-bad.org/chains/main/blocks/head/context/raw/json/contracts/index/KT1X61uV97BzmuKa2EG6mqMxje6gcbdJRGWs/used_bytes
• https://rollupnet.zaun.baking-bad.org/chains/main/blocks/head/context/raw/json/contracts/index/KT1X61uV97BzmuKa2EG6mqMxje6gcbdJRGWs/paid_bytes
• https://rollupnet.zaun.baking-bad.org/chains/main/blocks/head/context/raw/json/big_maps/index/0/total_bytes