Provide example docker-compose files that use the DockerHub images

[jmt-gh]

Summary

This PR provides an example docker-compose.yml file that leverages the images available on DockerHub. The motivation for this change is that the current examples only leverage building directly out of the repository, which isn't the most useful when looking to do an easy self hosted deploy. A minor side effect of this change was updating the directory structure in docker/ to make it more clear what the different use cases of the example docker-compose files is.

Ticket Link

N/A

[mattermod]

Hello @jmt-gh,

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[mattermod]

This PR has been automatically labelled "stale" because it hasn't had recent activity. A core team member will check in on the status of the PR to help with questions. Thank you for your contribution!

/cc @BenLloydPearson @aspleenic

[chenilim]

@jespino, can you help review this? I'm not super familiar with docker compose, and don't know how relevant these are. cc @sbishel.