Initial integration with go.step.sm/crypto

[maraino]

Description

This PR replaces some commands to use go.step.sm/crypto instead of github.com/smallstep/cli/crypto.

At some point, we should only go.step.sm/crypto (and go.step.sm/cli-utils), but having all commands migrated is not the objective of this PR.

[codecov[bot]]

Codecov Report

Merging #460 (90440fe) into master (9627abf) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 90440fe differs from pull request most recent head f3ae8cb. Consider uploading reports for the commit f3ae8cb to get more accurate results

@@           Coverage Diff           @@
##           master     #460   +/-   ##
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  Coverage   63.29%   63.29%           
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  Files          57       57           
  Lines        6863     6863           
=======================================
  Hits         4344     4344           
  Misses       2280     2280           
  Partials      239      239           

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