docs: Move all documentation, CI, and tooling to use `pie` instead of `pecl`

[bshaffer]

Thanks to grpc/grpc#42784 we can now install the grpc extension using pie instead of pecl:

pie install grpc/grpc-php-ext

This is because gRPC now maintains a new repo https://github.com/grpc/grpc-php-ext which publishes their extension package to https://packagist.org/packages/grpc/grpc-php-ext

NOTE: This is only available for gRPC. THe protobuf extension has NOT added PIE support yet. Support for protobuf is being tracked in protocolbuffers/protobuf#21808

[bshaffer]

See also: grpc/grpc#43051