[Platform][OpenRouter] Add Embeddings incl. example, fill Model catalog

[lochmueller]

This commit adds openrouter.ai features:

• Add the current set of models (without capabilities, because they are not checked)
• Add an Embeddings model + client and result converter to support embeddings
• Add an example for embeddings models
• Add error handling in the default ResultConverter of the completions endpoint to handle the "rate limit" of the free tier in a better way.

[chr-hertel]

if 429 is not accurate, just adopt it

Suggested change

	// In case free is running into 429 rate limit errors (note: it is a 404 error code in openrouter api), you can use the paid model:
	// In case free is running into 404 errors, you can use the paid model:

[chr-hertel]

Suggested change

	// Modelle
	// Models

[chr-hertel]

Happy to see openrouter get some attention - thanks for that 🙏

Left some minor comments, but close for merging 👍