[rastislavnemec]

Adds protoc-gen-connect-php from https://github.com/ftshp/connect-php, an unofficial PHP implementation of the Connect protocol (unary RPCs, PSR-18 client, PSR-15 server). For each service it generates an interface and a client class. It depends on protocolbuffers/php for the message classes, like connectrpc/go on protocolbuffers/go.

The Dockerfile follows connectrpc/go: static go install of the tagged module with -trimpath, scratch runtime, nobody user, on the current baseimages/Dockerfile.golang pin.

The plugin.sum files for eliza and petapis come from running the image against those two test images. The two streaming RPCs in eliza are skipped with a warning, which is intended. Say and the petapis services generate normally.

Closes #2851

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