docs: add a changelog file for the neon cli

[danieltprice]

I'd like to propose that we start keeping a changelog file for the Neon CLI. It will be helpful to reference this from the Docs and elsewhere. Ideally, we'll automate this as a next step, but I'd like to find an automated approach that we can use for all repos.

[alexfedosov]

I don't mind, but I'm not sure what value it adds compared to looking at the releases pages.
For example: https://github.com/neondatabase/neonctl/releases/tag/v2.0.0

The downside, however, is that it requires following one more process that can be automated. Maybe we can try to keep descriptions on the releases page nice and tidy instead?

For instance:

[duskpoet]

we have the semantic bot that generates release descriptions, we also have the committing watching so commits are following the conventional commits spec. We can reference releases or commits from docs, wouldn't that work?