feat (provider/perplexity): add support for return_images

[shaper]

Updated from #4621

[shaper]

@kevinwolfcr I don't actually get any images back from Perplexity, but it seems likely it's because I'm not a "Tier 2 user". I assume it's working for you, and I've only changed things formatting-wise, the core logic is the same as your original PR.

[lgrammel]

@kevinwolfcr can you confirm that the feature works for you end to end as a Tier 2 user?

[kevinwolfcr]

@shaper @lgrammel yes, I forgot to state that you must be part of tier 2. The images response is coming back, I am a tier 4 user.