[8.19] Fix FetchSourceContext serialization for mixed-version clusters

[jimczi]

Ensure the new exclude_vectors parameter is correctly serialized and deserialized when operating in a mixed-version cluster. Given that version 8.19 is not compatible with 9.0, we can assume that all versions on or after 9.1 will support this new parameter.

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[benwtrent]

Given that version 8.19 is not compatible with 9.0,

I don't understand how this is broken.

@thecoop could you take a look here?

[jimczi]

I don't understand how this is broken.

Using isPatchFrom is not enough since 9.1 can also send or receive data from 8.19. That's why I replaced isPatchFrom with onOrAfter. This is not technically correct, lots of versions, after the one I added, are not compatible with this change. However, the next version compatible with 8.19 is 9.1 so we can ignore them and keep the logic simple.

[benwtrent]

Using isPatchFrom is not enough since 9.1 can also send or receive data from 8.19.

I don't understand why this isn't enough. 9.1 should negotiate the appropriate transport version, and 9.1 should know about the patch version.

[thecoop]

Changing to onOrAfter is more semantically correct, as from the perspective of 8.19, the functionality represented by that version never goes away (there will never be a future transport version seen by 8.19 for which the isPatchFrom will turn the functionality off). The code in 9.1 is unchanged by this PR, and that knows how to handle the patches. In practice, it makes very little difference. As Ben says, 9.1 & 8.19 will negotiate a transport version that 8.19 understands anyway, and 9.0 is banned from forming a cluster with 8.19.

[benwtrent]

Thank you @thecoop for digging into this.

Looks good to me @jimczi