docs: Add documentation on distro stores

[raghotham]

🚀 Describe the new functionality needed

The llama stack distro server has several stores for state:

1. kvstore - for routing info
2. sqlstore - to store chat completion and responses
3. telemetry store - to store logs

We need to clearly document what is needed to spin up a distro server with these stores. Specifically, we need to make sure all of these stores can be served by a single postgres server (can be multiple dbs).

💡 Why is this needed? What if we don't build it?

We need to simplify our deployment steps

Other thoughts

No response