fix(relation): Add a "_bis" if relation already exists

This is the behavior for dataproperty and class, then let's use
the same strategy here
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Status Name Job ID Coverage
  Lint
passed black #465733
lint black

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passed check-manifest #465735
lint check-manifest

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passed flake8 #465732
lint flake8

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passed mypy #465734
lint mypy

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  Tests
passed py3 #465736
tests py3

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