Query rules: Check if MGET request failed when we retrieve query rules

[ioanatia]

closes #123429

when we retrieve the query ruleset, for each MultiGetItemResponse that represents a query rule, we need to explicitly check if retrieving the item failed.

[elasticsearchmachine]

Pinging @elastic/search-eng (Team:SearchOrg)

[elasticsearchmachine]

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

[Mikep86]

Can we add a test for the failure case?

[ioanatia]

I am not sure how to add a test for this.
I looked into RuleQueryBuilderTests whether I can change the current simulateMethod, but it does not seem doable.
For one, simulateMethod is reused in tests - and also it does not receive an argument that would us differentiate when we should return a failed MultiGetItemResponse vs a valid query ruleset.

I also looked at SemanticQueryBuilderTests thinking that it will test for some of the exceptions that can be raised in SemanticQueryBuilder, like when we fail to retrieve the inference result or deal with multiple inference results.
I hoped that SemanticQueryBuilderTests would have a model on how to mock these calls to the inference service, but I couldn't find them.

[kderusso]

LGTM, thanks for fixing!

[kderusso]

Nitpick - we probably can omit the headers for this test

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	9.0
✅	8.18
✅	8.x