Fix empty state field in /api/deprecated-features/used endpoint (backport #15042) (backport #15058)

[mergify]

The /api/deprecated-features/used endpoint was returning an empty state field in the JSON response. This was a regression introduced in #14229, which added the state field to show whether deprecated features are permitted or denied.

The issue was that rabbit_depr_ff_extra:cli_info0/1 always tried to extract the state field with a default empty string, even when rabbit_deprecated_features:list(used) doesn't include a state field (unlike list(all) which does).

This commit fixes the issue by only including the state field when it exists in the feature properties, using maps:find/2 and maps:merge/2 to conditionally add it.

The fix ensures that:

• /api/deprecated-features returns state field with valid values
• /api/deprecated-features/used omits the state field entirely

Tests are updated to verify this behavior.

GitHub issue: #14340

Proposed Changes

This PR fixes a regression introduced in #14229 where the /api/deprecated-features/used endpoint was returning an empty state field in the JSON response.

The Problem:

• PR Show current state of deprecated features (backport #14227) #14229 added a state field to show whether deprecated features are permitted or denied
• The rabbit_deprecated_features:list(all) function includes the state field, but list(used) does not
• However, rabbit_depr_ff_extra:cli_info0/1 always tried to extract the state field with a default empty string, resulting in "state": "" in the response for the /used endpoint

The Solution:

• Modified rabbit_depr_ff_extra:cli_info0/1 to conditionally include the state field only when it exists in the feature properties
• Used maps:find/2 and maps:merge/2 for a more idiomatic Erlang approach
• Updated tests to verify that:
  • /api/deprecated-features includes the state field with valid values (permitted or denied)
  • /api/deprecated-features/used omits the state field entirely

This ensures the API response matches the expected behavior: the state field is either set correctly or omitted, never empty.

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• Breaking change (fix or feature that would cause an observable behavior change in existing systems)
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• I have added tests that prove my fix is effective or that my feature works
• All tests pass locally with my changes
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This is an automatic backport of pull request #15042 done by [Mergify](https://mergify.com).

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This is an automatic backport of pull request #15058 done by [Mergify](https://mergify.com).