How do I install a php extension with pecl?

1. Download the pecl bash script specifically created for Upsun environments and put it in your source code.

2. From then on, you can use the pecl tool to install packages. For example:

   in .platform.app.yaml:

   hooks:
     build: |
       set -e 
       chmod +x pecl 
       pecl install grpc

More info: https://github.com/matthiaz/platformsh-tools#pecl