modules/programs/ssh: support pubkeyAuthentication

[augtheo]

Description

Allow configuring PubkeyAuthentication in the ssh config through module options.

This is a pretty straight-forward module-option -> config key change.

Checklist

• Change is backwards compatible.

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[ambroisie]

This PR looks fine.

However, we should migrate to a freeform module, to avoid even more PRs in the future (this isn't the first one).

[teto]

same situation as in #8073. While the PR is fine, once it's merged, it will add an additional migration path when implementing freeform module (grep "freeformType" in source code to see examples).
Would you be interested in doing such a migration ?