Create Dataset readers for BC5CDR in BLUE Benchmark

[hunterhector]

Is your feature request related to a problem? Please describe.
To prepare medical NER detection, we need to create a reader for the BC5CDR in the BLUE Benchmark: https://github.com/ncbi-nlp/BLUE_Benchmark

Describe the solution you'd like

1. Develop a reader for BC5CDR
2. Annotate the Entity Mentions from the dataset.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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