Adds protobuf and grpc PHP modules to web-container. This allows to create clients to interact with external gRPC services.

The installation can take some minutes, because the modules are compiled during the Docker image creation.

The following command should print the two compiled modules.

ddev exec php -m | grep -i 'grpc\|protobuf'

An example project can be found here: https://github.com/cmuench/grpc-demo/tree/master/examples/php

Contributed by @cmuench