enhancement: add @index_query access in actions

[Paul-Bob]

Description

This PR introduces access to the @index_query variable within the handle method. This variable represents the index query of the resource, making it easier to work with the full dataset under various conditions:

• When "select all" is enabled, @index_query == @query.
• When "select all" is not enabled, @query reflects only the selected records, whereas @index_query always returns the full index query with all filters and scopes applied.

This is particularly useful for standalone actions that need to operate on the entire dataset as defined by the current index query. For example, if a user applies filters and scopes, then selects "Export All", the action can directly access the fully filtered query via @index_query without relying on manual selection handling.

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

Screenshots & recording

Manual review steps

1. Step 1
2. Step 2

Manual reviewer: please leave a comment with output from the test if that's the case.

[codeclimate]

Code Climate has analyzed commit 5ace370 and detected 0 issues on this pull request.

View more on Code Climate.

[github-actions]

This PR has been merged into main. The functionality will be available in the next release.

Please check the release guide for more information.