Add GRPC Buffer Size to the Configmap (kubernetes#11155)

* feat: add grpc buffer size in the nginx template

* feat: add grpc buffer size in the configmap struct

* feat: add test for GRCP buffer size configuration in the configmap

* chore: add documentation for the grcp buffer size configuration

* fix: fix the copyright year of the test

* fix: fix import order

* fix: fix ignore for the linter - reason was missing

* chore: seems like we don't need to ignore the error handling

Author: StuxxNet