allow clear_origin in safe xcm builder (#4777)

Fixes #3770 

Added `clear_origin` as an allowed command after commands that load the
holdings register, in the safe xcm builder.

Checklist
- [x] My PR includes a detailed description as outlined in the
"Description" section above
- [x] My PR follows the [labeling
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- [x] I have made corresponding changes to the documentation (if
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- [x] I have added tests that prove my fix is effective or that my
feature works (if applicable)

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Co-authored-by: Francisco Aguirre <[email protected]>
Co-authored-by: gupnik <[email protected]>