gRPC-iOS Client Install Test

[dennycd]

Installation test measuring the following aspect

• Total package download time (Cocoapod & SPM)
• Total package build time (gRPC Pods and SPM Targets)
• Built binary size

This ensures we monitor overall client usage experiences and track regressions in build time & binary size.

In addition, the ability to parameterize our test scripts to target a specific branch or revision