Typeless index call can fail against an index with a custom type.

[jtibshirani]

Using the typeless index APIs can result in an error when the index contains a custom type name that is not _doc. The issue seems to arise when the index call introduces a mapping update.

The following gist demonstrates the problem: https://gist.github.com/jtibshirani/0929faf60bd78c794aeb01cc08d04c73.

The same issue also applies to typeless document update calls.

[elasticmachine]

Pinging @elastic/es-search

[jtibshirani]

@jpountz would you be able to look at this issue, as a continuation of #35790?

CC @urso

[benwtrent]

I ran into this same issue when calling a typeless _reindex against an index that had dynamically created fields.

Recreation steps: https://gist.github.com/benwtrent/2e3ea1e87746f58f557898869fd95e77

[jpountz]

@jtibshirani Absolutely, I'm putting it on top of my TODO list.