Enable `rpe` methods in bert-like models
# What does this PR do ?
- Add extrapolatable position embedding to bert-like model, based on the recent changes introduced in #6666 
- I am already using this change in the BioNeMo framework and running experiments to test how `rpe` techniques help bert-like model to extrapolate to longer sequences. 

**Collection**: [NLP]

# Changelog 
- BERT: 
   - nemo/collections/nlp/models/language_modeling/megatron_bert_model.py
   - nemo/collections/nlp/models/language_modeling/megatron/bert_model.py
# Usage

```python
model.position_embedding_type='' # Options ['learned_absolute', 'rope', 'alibi', 'xpos', 'sandwich', 'kerple']
```

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**PR Type**:
- [x] New Feature
- [ ] Bugfix
- [ ] Documentation

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# Additional Information
* Related to # (issue)
