Optimize cosmos db lookups

[prasjaiswal]

NOTE: It probably matters very less now, but we cannot batch read cosmos db because the URLs will land up in different partitions. Using same partitions for similar sites etc will run into hotspot issues etc. But we have following significant performance improvement here anyways.

1. Change SQL based cosmos db lookups to point lookups. Point lookups are way faster because it is using key part of <key, value> system to lookup a value (instead of some field of value). We can achieve this by looking up and storing up hashed URL (raw URL cannot be stored due to special characters)
2. Parallelize the cosmos db lookup calls. This helps with network latency significantly as the network delays for individual requests overlap.