Add dense retrieval

[DelaramRajaei]

• Add Colbert
• Change read and write queries
• Update yaml and requirement.txt
• Reformat code

[DelaramRajaei]

@hosseinfani I added the backtranslation results on 10 languages across 5 datasets.

[hosseinfani]

@DelaramRajaei you put the output folder outside ./qe. please put the result of backtranslations in ./qe/output/backtranslation/