test: register substratools function with decorator

[ThibaultFy]

CHANGE SUBSTRATOOLS IMAGE BEFORE MERGE

Companion PR:

• https://github.com/Substra/substra-tools/pull/65 (MAIN)
• https://github.com/Substra/substra/pull/310
• https://github.com/Substra/substrafl/pull/37
• https://github.com/Substra/substra-documentation/pull/202
• https://github.com/Substra/substra-tests/pull/225

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Summary

Notes

Please check if the PR fulfills these requirements

• [ ] If necessary, the changelog has been updated
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)
• [ ] The commit message follows the conventional commit specification
• For any breaking changes, companion PRs have been opened on the following repositories:
  • [ ] substra-tests
  • [ ] substrafl
  • [ ] substra-documentation