Update warning message for multiple databases availability

What does this MR do and why?

Updating the warning message with an indication when we expect general availability, as we have started to receive comments such as this one that indicate users expect this feature to be ready. We still want to keep the already published deprecation notice to inform users of this change early, so that they can plan their migration accordingly.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.