Update Cloudflare Workers Sites deployment documentation

[ben-xD]

Description

• Remove references to Workers KV (key value store). This was never used/ beneficial for Gatsby deployments because it doesn't use KV. It's also free now, not $5. I suspect it was added because of this, but we are not using an existing worker to serve these files and we're not using the KV api's (import { getAssetFromKV } from "@cloudflare/kv-asset-handler").
• Add step about npm run build because wrangler publish uploads local files, so it needs to be there.
• Added alternatives: Gatsby Hosting and Cloudflare Pages

Note: I was not able to build the doc site, so I cannot confirm that the markdown links ([Gatsby Cloud Hosting](/docs/how-to/previews-deploys/hosting/deploying-to-gatsby-cloud.md)) are going to work.

Related Issues

Addresses the issue raised in #31103

[KyleAMathews]

Thanks!