Generate server diff in CI (#835)

    echo "Current branch resolved to: $current_branch"

    gen_branch="__generated-$current_branch"

    repo_root=$(git rev-parse --show-toplevel)

	cd "$repo_root" && ./gradlew :aws:sdk:assemble

    target="$(mktemp -d)"

    # Generate and copy AWS SDK models

    cd "$repo_root" && ./gradlew :aws:sdk:assemble

    mv "$repo_root"/aws/sdk/build/aws-sdk "$target"

    # Generate and copy codegen-server-test models

    cd "$repo_root" && ./gradlew :codegen-server-test:assemble

    mv "$repo_root"/codegen-server-test/build/smithyprojections/codegen-server-test "$target"/server-test

    # Cleanup the server-test folder

    rm -rf "$target"/server-test/source

    find "$target"/server-test |grep -E "smithy-build-info.json|sources/manifest|model.json" | xargs rm -f

    # checkout and reset $gen_branch to be based on the __generated__ history

    git fetch origin "$base_branch"

    git checkout -B "$gen_branch" origin/"$base_branch"

    cd "$repo_root" && git rm -rf .

    rm -rf "$repo_root/aws-sdk"

    rm -rf "$repo_root/server-test"

    mv "$target"/aws-sdk "$repo_root"/.

    mv "$target"/server-test "$repo_root"/.

    git add "$repo_root"/aws-sdk

    git add "$repo_root"/server-test

    PRE_COMMIT_ALLOW_NO_CONFIG=1 git \

        -c "user.name=GitHub Action (generated code preview)" \

        -c "user.email=generated-code-action@github.com" \