Automatically put OpenAI key in the secret storage

[dividedmind]

We have "set openai key" command to put the OpenAI key in secret storage, but it's not very discoverable and users sometimes put it in an env variable instead. It should be possible to automatically catch that and redirect to the storage; I'd suggest then replacing the key in the displayed environment with <secret> or ****** or ∙∙∙∙∙ or ●●●●●● or something to indicate it's set.