Add capabilities to fetch ssh dependencies by passing an ssh key

[nagua]

Checklist

• I have read the Contributor Guide
• I have read and agree to the Code of Conduct
• I have added a description of my changes and why I'd like them included in the section below

Description of Changes

Currently there is no way in cargo-deny-action to fetch and evaluate ssh dependencies (see #67).
I order to enable the feature this PR introduces four changes:

1. A new action input to pass a private ssh-key for ssh authentication
2. A new action input to pass ssh known hosts so a ssh connection can be established
3. A new action input to use the git cli instead of the build in cargo fetcher to enable ssh git repositories
4. It adds openssh to the Docker image to allow git to use ssh for cloning

It also updates the rust + cargo_deny version. If you wish to separate these changes, feel free to
change this.

Related Issues

Fixes #67

[umgefahren]

Is there any way this could work with webfactory/ssh-agent? I tried this PR in our CI and it doesn't work. However I have other jobs using ssh-agent where it does work.

[nagua]

I don't have much experience with ssh-agent. So I would need to investigate that. You would probably need to pass the ssh-agent socket or something like that into the container.

[Jake-Shadle]

So does this PR actually work, or only in some cases? If it doesn't work in all cases I would be hesitant to merge this because I personally don't need this feature and would then need to rely on contributors to fix/improve it since I wouldn't notice when/how it was broken.

[nagua]

@Jake-Shadle I'm not sure what you mean with that. Whenever you have an ssh key that you can pass around as a string to the github action you can use this PR to access crates via ssh. You can currently only use one ssh-key and you cannot use ssh-agent. But I don't know if there is a use-case for that or how it could be implemented.

@umgefahren I looked at that github action and I cannot see a way how this could work with the cargo-deny action. The cargo-deny action spawns a new docker container via the actions.yml. For this to work we would need to mount the SSH_AUTH_SOCK socket into the container. But as far as I can see github doesn't let you specify additional mounts for a docker based action. The only way that I can currently see would be to completely rewrite the action and spawn the container in a host based script ourself.

The only thing we could currently discuss if we need to support more than one ssh-key.

[Jake-Shadle]

If someone needs multiple keys they can make a PR.