Add ppc64le architecture to release script

[Jenkins-J]

Add ppc64le architecture to releases. This is necessary for the rules_buf bazel module to work properly on the ppc64le architecture as a binary release is required by the rules_buf_toolchains target.

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[doriable]

Since we would not need to provide an additional env var for the ppc64le build (e.g. GOARM for the arm7 binary), we could something similar to what you've done below in the else clause (and would not need to add a repeated build statement here):

      else
        if [ "${arch}" == "ppc64le" ] && [ "${os}" != "Linux" ]; then
          continue
        fi
        CGO_ENABLED=0 GOOS=$(goos "${os}") GOARCH=$(goarch "${arch}") \
          go build -a -ldflags "-s -w" -trimpath -buildvcs=false -o "${dir}/bin/${binary}${extension}" "${DIR}/cmd/${binary}"
      fi