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

Thanks to https://github.com/grpc/grpc/pull/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 https://github.com/protocolbuffers/protobuf/issues/21808

No specific files or tests are named. Search the documentation, CI configuration, and tooling for pecl references; update gRPC installation guidance and automation to use pie while keeping protobuf on pecl, then verify the relevant checks and remaining references.

Written by the indexing model from the issue text.