fix: fix perplexity API

[irscin]

The perplexity API models are not available anymore and return 400 API errors. I replaced the models in the settings template file with the current ones available according to the official docs at: https://docs.perplexity.ai/getting-started/models

Steps to reproduce

1. Type mods --settings in the terminal and ENTER
2. Add a Perplexity API key.
3. Change the default model to any Perplexity model.
4. Try to use mods. mods 'Hey, are you doing?'
5. Get an error 400 API, model does not exist.

• [X] I have read CONTRIBUTING.md.
• [X] I have created a discussion that was approved by a maintainer (for new features). <- Not necessary, since this is a bug fix, not a new feature.

[cip8]

The default config for Perplexity was outdated, indeed! 👏

Two comments on the PR:

• a fallback to the cheaper sonar could be useful
• i don't think an alias with the same name should be added

[irscin]

@cip8 Changes implemented.

• Redundant aliases removed
• Fallbacks added