[DOCS] Correct source.index parm def in reindex API

[jrodewig]

Corrects the source.index request body parameter definition to
state that arrays, not comma-separated values, are accepted.

Relates to #51949

[elasticmachine]

Pinging @elastic/es-docs (>docs)

[elasticmachine]

Pinging @elastic/es-distributed (:Distributed/Reindex)

[henningandersen]

I think we should just support the "," notation instead to try to align with the multiple indices documentation. This is also how snapshot/restore works.

[henningandersen]

Opened #52044 to fix this.

[jrodewig]

Thanks @henningandersen. However, I think this would still be a relevant docs update for 7.6 7.5 and 6.8.

I've changed the target branch and updated the labels appropriately.

[henningandersen]

LGTM.

Ideally, we should backport the fix from #52044 to 6.8 too, but given that there is such an easy workaround and the code changed a lot between 6.8 and 7.x, I think just updating the docs instead in 6.8 is fine.

I am not sure about 7.5 though, given that 7.6 is now released, I assume we should only do this for 6.8? The next 7.6 release will contain the fix.

[jrodewig]

Thanks @henningandersen. After taking a closer look at the 6.8 docs, I believe this is already documented pretty well:

I'll close this PR. Thanks for fixing this!