Expand fetch phase profiling to support inner hits and top hits aggregation phases

[andrevandeven]

Description

There are 3 types of fetch phases that are important to account for in profiling:

• Standard fetch phase: This is the fundamental second stage of every standard search query. It's a broad operation that retrieves the full source document (_source) for the top-ranking documents identified in the initial query phase.
• Inner Hits Fetch: This is a specialized type of fetch used to pinpoint exactly why a document with nested or parent-child data matched your query. It retrieves the specific nested objects that caused the match, not just the top-level document.
• Top Hits Aggregation (Fetch Top Hits): This is not a phase of the search itself, but rather a powerful aggregation. It allows you to fetch the top-matching documents per group or per bucket after a primary aggregation has run.
  In the first stage of implementation, the fetch phase profile only supports profiling the standard fetch phase.

This change allows inner hits fetch and top hits aggregation fetch to be profiled and included as separate fetch phases alongside the standard fetch phase in the profile. If multiple separate inner hits searches are run or top hits aggregations are run, they will appear as separate breakdowns. Each individual fetch phase within a search or aggregation will be consolidated under the breakdown of its respective operation rather than creating a new breakdown for each individual fetch phase that is run. The logic for this is that top hits aggregation often runs fetch phase many times, depending on the number of documents aggregated, and lack of consolidation would lead to a verbose and crowded search profile.

Related Issues

Resolves #18862

#18864

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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✅ Gradle check result for 9738ccb: SUCCESS

[andrevandeven]

@msfroh I updated the rest tests to skip versions before 3.3, so should be good to go now! EDIT: Gradle check needs to run again because I fixed changelog merge issues. Will ping again when it finishes running!

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✅ Gradle check result for 2ed7df4: SUCCESS

[andrevandeven]

@msfroh good to go now!