Spring Boot 2.3.0.M2 release

Spring Boot 2.3.0 second milestone release, from the landmark warehouse acquisition.

This is a major milestone highlights include: 

• Improved Docker Mirroring Support
• Upgrade to MongoDB 4 (still in beta)
• Support of the wildcard position profile
• Many dependencies upgrade 

For details, see:

https://spring.io/blog/2020/02/13/spring-boot-2-3-0-m2-available-now 

https://github.com/spring-projects/spring-boot/releases/tag/v2.3.0.M2