Provide a top-level "Deploy an app/agent" doc

[jhaaaa]

Feedback from agent devs:

1. I think we need a 'Deploy your app/agent' section of the docs at the top level. It's not intuitive that you'll learn about these deploy details in this tutorial: https://docs.xmtp.org/agents/build-an-agent#deploy-an-agent

2. Following this in the tutorial is great. Just difficult to find when you're deploying and not following this tutorial directly: https://docs.xmtp.org/agents/build-an-agent#deploy-an-agent

3. I got stuck here as well. Examples repo was good but it’d be nice to have examples for deployment on aws/gcp/azure/railway/flyio/cloudflare containers.

4. It makes sense that you need to persist the db file between builds but not clear how to do that necessarily

• Use persistent storage