Add BE-PEPPOL example

[alvarolivie]

• Add a BE PEPPOL example

Pre-Review Checklist

• I've read the CONTRIBUTING.md guide.
• N/A I have performed a self-review of my code.
• N/A I have added thorough tests with at least 90% code coverage.
• I've modified or created example GOBL documents to show my changes in use, if appropriate.
• N/A When adding or modifying a tax regime or addon, I've added links to the source of the changes, either structured or in the comments.
• I've run go generate . to ensure that the Schemas and Regime data are up to date.
• N/A All linter warnings have been reviewed and fixed.
• N/A I've been obsessive with pointer nil checks to avoid panics.
• N/A The CHANGELOG.md has been updated with an overview of my changes.
• Requested a review from @samlown.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.22%. Comparing base (9593fec) to head (cea871f).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #537   +/-   ##
=======================================
  Coverage   90.22%   90.22%           
=======================================
  Files         286      286           
  Lines       15862    15862           
=======================================
  Hits        14312    14312           
  Misses       1231     1231           
  Partials      319      319           

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[samlown]

The Supplier and Customer do not have a participant ID (inboxes), so as an example for Peppol, it probably needs a bit more work...