feat: determine autoshard for a given content topic

[adklempner]

This is a feature request

Problem

In order to determine the pubsub topic to use for a content topic in the context of autosharding, we need to map the content topic to a shard number using the following algorithm: https://rfc.vac.dev/spec/51//#algorithm

Proposed Solutions

Add a function to utils, which, given a string and number of shards:

• validates that the string is a valid content topic
• parses application and version fields from the string
• SHA-256 hash the concatenation of the UTF-8 string bytes of the application and version fields
• perform hash mod numShards to determine which shard index to use

Notes

only use the last 64 bits of the hash when performing modulo step