Support Spring Boot `application.properties` in `fromEnv()`

[bnbarak]

Currently, the fromEnv() factory only reads from process environment variables (e.g. OPENAI_API_KEY, OPENAI_BASE_URL). It would be very useful for Spring Boot apps if it also picked up properties defined in application.properties / application.yml, such as:

openai.api-key=sk-...
openai.base-url=https://api.openai.com/v1

That way, users can centralize all configuration in Spring’s standard config files rather than exporting separate OS-level env vars.

Thank you!

[TomerAberbach]

For inspiration, AWS looks up system properties followed by environment variables

https://sdk.amazonaws.com/java/api/latest/software/amazon/awssdk/auth/credentials/DefaultCredentialsProvider.html