Add interoptesting for Tectia SSH keys.

[dumol]

Ditto, enable testing loading SSH keys generated by Tectia's ssh-keygen-g3.

The Tectia tests are written, but not executed, as there's no Tectia on GitHub's own runners.

P.S. Actually only loading Tectia-generated keys tests are written, not loading our keys with Tectia.

[adiroiban]

One idea, run the tests inside a docker image which has Tectia SSH installed with our licence.

The docker image can be hosted inside our Chevah private organization Docker registry provided by GitHub - https://github.com/features/packages

The chevah-keycert job can download the image from the private registry and run the tests.
I don't think that this will conflict with your development licence that we have from Tectia.

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As the same time. Does ssh-keygen-g3 require a valid licence?

Maybe only the sftp / ssh / sshd command will require a licence and we can use ssh-keygen-g3 with the evaluation licence... I don't know. Just a crazy idea.