Feature/32 OpenAI key configuration from content

[stoerr]

This sets up lookup for the OpenAI API Key via Sling Context Aware Configuration, and adds a configuration so that it can set up in AEMaaCS as cloud secret.

We have now a fallback hierarchy for the OpenAI API key:

• Sling Context Aware Configuration
• OSGI configuration at "Composum AI GPT Chat Completion Service" - this is configured by default for AEMaaCS
  as $[secret:OPENAI_API_KEY] to retrieve a value configurable in the cloud manager
• Environment variable OPENAI_API_KEY

For the sling context aware configuration, we have a configuration
com.composum.ai.backend.slingbase.model.OpenAIConfig with the property openAiApiKey . Thus, set up configuration of
the API key in the JCR repository has the following possibilities:

• to enable it globally (even if you do not normally use Sling Context Aware Configuration), you could set up a
  configuration node at
  /conf/global/sling:configs/com.composum.ai.backend.slingbase.model.OpenAIConfig
  with the property openAiApiKey set to the OpenAI API key. Caution: this requires read permissions for the users.
• to enable it for a site or page tree that already has a sling:configRef set up (searchable with query
  /content//*[@sling:configRef]) you could set up a configuration node
  com.composum.ai.backend.slingbase.model.OpenAIConfig in
  the corresponding /conf/.../sling:configs node.
• otherwise you'd have to set up Sling Context Aware Configuration for the page tree in question.