feat: validate content topics in encoder and decoder

[adklempner]

This is a feature

Problem

all content topics in js-waku are treated as strings without any validation. According to spec for autosharding, the content topics MUST follow the specified format: https://rfc.vac.dev/spec/51/#content-topics-format-for-autosharding

Proposed Solutions

Create a function that validates a content topic based on the specified format

Use the function to validate any content topics used to create an encoder or decoder IF the node is setup to use autosharding

Notes

We want to continue to use content topic as a string in order to not introduce many breaking changes, but we will validate it in the most important spots

[adklempner]

I've made a PR that adds the function to validate a content topic: #1711

However, it shouldn't actually be used in encoder/decoder until we add a config which determines whether or not the node uses autosharding or static sharding