release-25.1: server: fix admin server Settings RPC redaction logic

[blathers-crl]

Backport 1/1 commits from #138688 on behalf of @kyle-a-wong.

/cc @cockroachdb/release

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Previously admin.Settings only allowed admins to view all cluster settings without redaction. If the
requester was not an admin, would use the isReportable field on settings to determine if the setting should be redacted or not. This API also had outdated logic, as users with the MODIFYCLUSTERSETTINGS should also be able to view all cluster settings (See #115356 for more discussions on this).

This patch respects this new role, and no longer uses the isReportable setting flag to determine if a setting should be redacted. This is implemented by query crdb_internal.cluster_settings directly, allowing the sql layer to permission check.

This commit also removes the unredacted_values from the request entity as well, since it is no longer necessary.

Ultimately, this commit updates the Settings RPC to have the same redaction logic as querying crdb_internal.cluster_settings or using SHOW CLUSTER SETTINGS.

Epic: None
Fixes: #137698
Release note (general change): The /_admin/v1/settings API now returns cluster settings using the same redaction logic as querying SHOW CLUSTER SETTINGS and crdb_internal.cluster_settings. This means that only settings flagged as "sensitive" will be redacted, all other settings will be visible. The same authorization is required for this endpoint, meaning the user must be an admin or have MODIFYCLUSTERSETTINGS or VIEWCLUSTERSETTINGS roles to hit this API. The exception is that if the user has VIEWACTIVITY or VIEWACTIVITYREDACTED, they will see console only settings.

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Release justification:

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

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  issues or test-only changes.
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[cockroach-teamcity]

This change is