Add Kushagra as CODEOWNER for Cosmos (Azure#2800)

I didn't realize you weren't already there ;)

Author: analogrelay

.github/CODEOWNERS

@@ -63,7 +63,7 @@
 # ServiceOwner: @Pilchie
 # ServiceLabel: %Cosmos
 # PRLabel: %Cosmos
-/sdk/cosmos/             @analogrelay @Pilchie @kirankumarkolli @tvaron3 @FabianMeiswinkel @kundadebdatta @nehrao1
+/sdk/cosmos/             @analogrelay @Pilchie @kirankumarkolli @tvaron3 @FabianMeiswinkel @kundadebdatta @nehrao1 @kushagraThapar
 
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 # Eng Sys