Create release artifacts for protoc-gen-connect-go

[emcfarlane]

Add release artifications using goreleaser for protoc-gen-connect-go.

Fixes #695

dist
├── artifacts.json
├── config.yaml
├── connect-go_1.15.0-SNAPSHOT-b581b2b_checksums.txt
├── metadata.json
├── protoc-gen-connect-go-v1.15.0-Darwin-arm64.tar.gz
├── protoc-gen-connect-go-v1.15.0-Darwin-x86_64.tar.gz
├── protoc-gen-connect-go-v1.15.0-Linux-aarch64.tar.gz
├── protoc-gen-connect-go-v1.15.0-Linux-x86_64.tar.gz
├── protoc-gen-connect-go-v1.15.0-Windows-arm64.zip
├── protoc-gen-connect-go-v1.15.0-Windows-x86_64.zip
├── protoc-gen-connect-go_darwin_amd64_v1
│   └── protoc-gen-connect-go
├── protoc-gen-connect-go_darwin_arm64
│   └── protoc-gen-connect-go
├── protoc-gen-connect-go_linux_amd64_v1
│   └── protoc-gen-connect-go
├── protoc-gen-connect-go_linux_arm64
│   └── protoc-gen-connect-go
├── protoc-gen-connect-go_windows_amd64_v1
│   └── protoc-gen-connect-go.exe
└── protoc-gen-connect-go_windows_arm64
    └── protoc-gen-connect-go.exe