Add more examples to the documentation

Currently the examples are very limited and mostly limited to search examples. The documentation should be improved to add examples for:
[elasticsearch.client.IndicesClient.put_mapping](https://elasticsearch-py.readthedocs.io/en/latest/api.html?highlight=mapping#elasticsearch.client.IndicesClient.put_mapping)
https://elasticsearch-py.readthedocs.io/en/latest/api.html?highlight=mapping#elasticsearch.client.IndicesClient.put_mapping
https://elasticsearch-py.readthedocs.io/en/master/api.html?highlight=watcher#elasticsearch.client.WatcherClient

Background: just updated my ES 7 to 8 and the python client scripts I had no longer work. After several hours plowing through the documentation I just gave up

Review the existing documentation examples and the linked IndicesClient.put_mapping and WatcherClient API pages first. Add practical examples for those APIs alongside the current search examples, and consider the Elasticsearch 7-to-8 migration context; done means the new examples are clear and rendered in the documentation.

Written by the indexing model from the issue text.