API work for adding group admin and deleting group admin

[Assadbintahir]

In this issue, we will do the work for adding group admin and deleting group admin

Expected Request and Response payloads can be found in the following design document:

https://docs.google.com/document/d/1_nU1UZaU3T9iIp-Xhf_k8RMaefjnom8LzOE_5_42xTQ/edit#

[dayemsiddiqui]

I have completed work on this issue. Assigning this to @Assadbintahir for testing

[jekram]

Thanks

[Assadbintahir]

I have tested this and it is working as expected

[jekram]

Thanks