doc: Explain how to use a persistent state disk with Docker

[teor2345]

Motivation

A user was surprised when their Docker run stopped and they couldn't find Zebra's state:

Hi guys, do you know how can I resume Zebrad's sync? I've installed it trough docker and stopped at block 550000. But now I can't find Zebra's files/folders.

https://discord.com/channels/809218587167293450/809251029673312267/1179106203868090378

It would be helpful to tell users how to set up a persistent state disk in the Docker guide:
https://github.com/ZcashFoundation/zebra/blob/main/book/src/user/docker.md

If we're going to change any configured paths inside the Docker image, we might want to do that first.

Specifications

https://docs.docker.com/storage/volumes/

Complex Code or Requirements

No response

Testing

Manually run the commands and check that the state is persistent.

Related Work

No response

[gustavovalverde]

@mpguerra this is what we talked about recently. So it might seem as we'll have to schedule it for next sprint, alongside:

• ci: create documentation on how to run tests locally for development purposes #4464
• Make it possible to run CI tests locally for developers #7534
• devops: Align tests names in CI, Docker and Rust code #7541

As all these will require a similar work.

* It seems #4464 and #7534 are basically the same.

[mpguerra]

Hey team! Please add your planning poker estimate with Zenhub @arya2 @gustavovalverde @oxarbitrage @teor2345 @upbqdn