bug fix - alibi causal: for ith query, bias is m · [−(i − 1), ..., −2, −1, 0] for the first i keys
# What does this PR do ?

Fix alibi position embedding for causal attention. 


**Collection**: NLP

# Changelog 
Existing: returns (1, num_heads, 1, key_length)
Fixed: returns (1, num_heads, query_length, key_length), where for ith query, the bias is m · [−(i − 1), ..., −2, −1, 0] for the first i keys, as per the alibi paper
  
**PR Type**:
- [ ] Bugfix


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# Additional Information
* Related to # (issue)
