Add Support for Open Router API Keys

[TeenBiscuits]

Could be nice to see the usage in your Open Router API Keys

[steipete]

Not sure how that'd map to subscription tracking, but open to look at designs/PRs!

[BitCalSaul]

same here

[TeenBiscuits]

For context, when you create API keys in Open Router, you can set up budgets (aka credits limits) for each key:

So you could add your API keys to the Codex bar to get the usage left and reset time for each key, to control your usage.
In the OpenRouter docs, it is explained how you can get the usage with a single API request for each key. OpenRouter Docs

[rublagar]

There is a related PR available here: #298