Add rsa-sha2-512 and rsa-sha2-256, keys

[emmanuel-thinkst]

Proposed changes

There has been issues the open-canary ssh server, not being able to complete an ssh connection with some clients if they don't offer the "Host Key Algorithms" ssh-rsa and ssh-dss. (#186)
After some testing we found out that, usually if the "Host Key Algorithms" above are not offered, a client would then offer these Algorithms, rsa-sha2-512 rsa-sha2-256, instead.
These changes add support for the "Host Key Algorithms" rsa-sha2-512 rsa-sha2-256, to the open-canary ssh server.

Types of changes

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• [ x] Bugfix (non-breaking change which fixes an issue)
• [ x] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update

Checklist

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• [ x] I have added tests that prove my fix is effective or that my feature works
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