UpdateRequest need toString()

[zzt93]

Describe the feature:
When using the Java API to do the update/index/delete, I log the request for debug. But the UpdateRequest not implemented the toString() method, which causes some inconvenience.

[DaveCTurner]

Thanks for the report. This does seem to be the case. It shouldn't be too hard to add this - would you care to submit a PR?

[cybrooke]

I would like to do this as my first contribution if @zzt93 doesn't want to.

[DaveCTurner]

Go for it, @cybrooke.

[zzt93]

@cybrooke Actually I implement a version, which suits my need and much like IndexRequest and DeleteRequest. Anyway, it's up to @DaveCTurner to decide which one to use.

[DaveCTurner]

I reviewed and left comments on both PRs. I think #27997 is the way to go. Thanks both, and apologies for the race that led to the duplicated effort.