Adding a Dockerfile to run keepassxc in a container

[auzias]

Description

The file Docker/Dockerfile can be used to build a Docker image.
To build the image and run a container see the file Docker/README.md.

Motivation and Context

This change is required in order to provide a community manage Docker image.

How Has This Been Tested?

The container has been tested using the commands shown in Docker/README.md.

Types of changes

• ✅ New feature (non-breaking change which adds functionality)

Checklist:

• ✅ I have read the CONTRIBUTING document. [REQUIRED]
• ✅ My code follows the code style of this project. [REQUIRED]
• ✅ All new and existing tests passed. [REQUIRED]

[phoerious]

I would prefer distributing only stable and signed releases as Docker images, not the current develop branch.

For building KeePassXC in a Docker container, we already have a Docker image based on Ubuntu 16.04. However, this still needs some work and we probably need to go back to CentOS 6.8 for best compatibility across the Linux landscape.

Also one issue we have when running KeePassXC inside a Docker container is that the UID inside the container must match the UID of the host if you don't want to run KeePassXC as root inside the container. Otherwise you can't write to the database file.

[droidmonkey]

Is this still required now that we have a docker container as part of the release script?

[phoerious]

I think this one is more intended to actually run KeePassXC. I'm not quite sure, though, where to put it in the source tree and how to properly distribute it.

[auzias]

It is indeed to run KeePassXC, not compile it. As for!

• where to put it: my guess is it's up to.
• how to distribute it... I'ld say http://hub.docker.com/

[phoerious]

After some more consideration, I still don't know where to put this. I would prefer having this Dockerfile on Dockerhub instead of our repository. I think that would be a better place.
We already have a Snap package which does about the same as a Docker container, only better.

[droidmonkey]

Recommend moving this to the packaging repo.

[droidmonkey]

Migrated over to keepassxc-packaging/#4