Migrate integration tests away from `bitnamilegacy/redis-sentinel`

Bitnami was taken over by Broadcom/VMWare/Tanzu and decided to only provide paid, security hardened images. Therefore the existing images have been moved to a legacy repository where they will not receive updates anymore.

- [How to prepare for the Bitnami Changes coming soon](https://community.broadcom.com/blogs/beltran-rueda-borrego/2025/08/18/how-to-prepare-for-the-bitnami-changes-coming-soon)
- https://github.com/bitnami/containers/issues/83267

It is best to migrate to another image repository for the integration tests:
https://github.com/influxdata/telegraf/blob/4054043bf6005ca5dfef76e8a10df9385eee7e3a/plugins/inputs/redis_sentinel/redis_sentinel_test.go#L359

The integration test is in plugins/inputs/redis_sentinel/redis_sentinel_test.go, around line 359; start by inspecting how it pulls and starts bitnamilegacy/redis-sentinel. Choose a maintained replacement image, update the test reference, and run the redis_sentinel integration tests to confirm they pass without the legacy image.

Written by the indexing model from the issue text.