Adding Igbo NER data 
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Thanks for the PR @purvimisal. 

Few comments below.  Hi, @lhoestq Thank you for the review. I have made all the changes. PTAL!  the CI error is not related to your dataset, merging
This PR adds the Igbo NER dataset.
Data: https://github.com/IgnatiusEzeani/IGBONLP/tree/master/ig_ner 
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