Add gRPC tools grpcurl and ghz

[Ka1wa]

Add the grpcurl and ghz packages to netshoot.

• https://github.com/fullstorydev/grpcurl
• https://github.com/bojand/ghz/

Ghz package contains both ghz and ghz-web but when I tried to run ghz-web I got the following error:

bash-5.0# ./ghz-web
Error relocating ./ghz-web: __memcpy_chk: symbol not found
Error relocating ./ghz-web: __memset_chk: symbol not found

Seems like an issue with Alpine and glibc? I personally only cared about ghz so I removed ghz-web to not make the container bigger unnecessarily.

[nicolaka]

Thanks for the PR. Can you please update the README to reflect the added tool and if it has any how-to then please add it there. Once you do that ( please rebase too since I bumbped alpine to 3.11) then i'll merge this PR>