text: Title: Improve structure of `admin.apps.config.set` HTTP API arguments
  Body: I improved the documentation and helped implement the API methods for `admin.apps.config.*` recently in the node-slack-sdk. As part of this work, it became clear that the arguments for the `admin.apps.config.set` method were vaguely documented and unclear.
  
  I did some discovery and was able to more specifically type them in the node-slack-sdk. See [this section of the PR in node-slack-sdk](https://github.com/slackapi/node-slack-sdk/pull/1676/files#diff-3cc91696a3000faca80f10afd29704e5e7aee229b13a431fc966f7d7ef1e3a4aR1046).
  
  Perhaps we could do something similar in the Python SDK.
  
  ### Category (place an `x` in each of the `[ ]`)
  
  - [x] **slack_sdk.web.WebClient (sync/async)** (Web API client)