SpringBoot Add a note about generating a unique DataSource name to the release notes

https://twitter.com/cpcolin/status/1261369053630754816?s=21

Comment From: Alok255

Hello, I am interested in the contribution. Is that only document fix? Or should we modify the source code?

Comment From: snicoll

Thanks for the offer @Alok255. This was a left over of the 2.3 release notes for which I've just added a section.