Add ability to choose branch to generate aws-sdk-rust/next from

# This workflow updates the `next` branch with freshly generated

# code from the latest smithy-rs and models that reside in aws-sdk-rust.

# Allow only one release to run at a time

concurrency:

  group: update-aws-sdk-next

  cancel-in-progress: true

name: Update `aws-sdk-rust/next`

on:

  workflow_dispatch:

    inputs:

      generate_ref:

        description: |

          Which branch/commit/tag of smithy-rs to use to generate aws-sdk-rust/next. Defaults to `main`.

        required: true

        type: string

        default: main

jobs:

  update-next:

      uses: actions/checkout@v3

      with:

        repository: awslabs/smithy-rs

        ref: main

        ref: ${{ inputs.generate_ref }}

        path: smithy-rs

    - name: Check out `aws-sdk-rust`

      uses: actions/checkout@v3