Fix size of "Redis/Sentinel - Persistent" for 25k

What does this MR do and why?

The 15k documentation uses a smaller instance than the 10k installation for the "Redis/Sentinel - Persistent2" component. I think that's a typo; it probably should be similar (or bigger) than 10k. 50k uses m5.xlarge.

Screenshots or screen recordings

This is 10k:

This is 25k:

This is 50k:

MR acceptance checklist

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I'm not sure if this change warrants a CHANGELOG entry, please let me know if it does.