WIP: Ledger PKI feature

[srasoamiaramanana-ledger]

Description

This PR defines the command and syscalls to enable the Ledger PKI feature.

Changes include

• Bugfix (non-breaking change that solves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.47%. Comparing base (e21f13e) to head (32c8a85).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #599   +/-   ##
=======================================
  Coverage   60.47%   60.47%           
=======================================
  Files          12       12           
  Lines        1723     1723           
=======================================
  Hits         1042     1042           
  Misses        681      681           

Flag	Coverage Δ
unittests	60.47% <ø> (ø)

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