Add shield hit and miss metrics
Six new metrics related to shield hits and misses have been added: shield_hit_requests, shield_miss_requests, shield_hit_resp_header_bytes, shield_hit_resp_body_bytes, shield_miss_resp_header_bytes, and shield_miss_resp_body_bytes.
Prior change: AssemblyScript SDK 0.5.0
Following change: Rust SDK 0.8.4
