FIXES FRMW-2878
**What**
Currently, the `one-to-one` unique constraints does not account for deleted record. This prevents from inserting a new record wth the same fk if another one is deleted.
**Caveat**
`hasOne` with FK option is meant to be a special case, for example a many to one - one to many without defining the other side of the relation. In that case we don't handle this behaviour and keep it as it is
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