WIP on FLS and Field Masking optimization

[cwperks]

Description

This PR revisits the data structure that carries the <concrete index> -> Set<String> maskedFields (or FLS) that is carried on the ThreadContext. Currently, the datastructure is carrying the entire evaluatedDlsFlsConfig which iterates through all roles and computes a map of concrete indices matching the mattern on any role -> the set of masked Fields or Fls.

An example data structure is like this:

{first-test-index=[lyrics::/(?<=.{1})./::*, artist::/(?<=.{1})./::*], second-test-index=[lyrics::/(?<=.{1})./::*]}

The problem with this is that if a request is only on a single index, this data structure will still contain all matched concrete indices -> set of maskedFields on the ThreadContext for every request.

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)

Enhancement

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

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