Retrofit upgrade to 2.6.0 which has the kotlin coroutines support

[bhavinmdesai]

Requirements

• Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions

Description of the Change

• Retrofit dependency has been upgraded to 2.6.0 which has the kotlin coroutines support

Alternate Designs

• None

Why Should This Be In Core?

• Better implementation

Benefits

• By merging this code, it will be easy to understand in the future as everything will be managed by single dependency Retrofit and retrofit2-kotlin-coroutines-adapter is no longer required

Possible Drawbacks

• None

Verification Process

• I have built and run the code and it is working exactly the same as before which means nothing is broken

Applicable Issues

• None