Refactor bias act fusion
Signed-off-by: MaximumEntropy <sandeep.subramanian.1@umontreal.ca>

# What does this PR do ?

Refactors bias activation fusion logic and adds the config option to the remaining yaml files.

**Collection**: [Note which collection this PR will affect]

# Changelog 
- Adds/replaces `bias_gelu_fusion` with `bias_activation_fusion` in remaining yaml configs.
- Refactors some of the logic within `transformer.py` and `lm_encoder_decoder.py`.

# Usage
N/A

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

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# Additional Information
* Related to # (issue)
