feat: Support Spring Boot 4.x

[kagkarlsson]

Add support for Spring Boot 4.x. Most likely need to create a new artifact for sb4-support. Not sure what to do with the duplication (is it possible to use maven shading to move shared classes into both starters?)

db-scheduler-spring-boot-starter (the current one, for 3.x)
db-scheduler-spring-boot-4-starter (new)

[beilCrxmarkets]

@kagkarlsson
I can contribute to the Spring Boot 4 migration.
Proposed Project Structure:

• db-scheduler
• db-scheduler-spring-boot-starter-parent
  • db-scheduler-spring-common # Common classes shared between SB3 & SB4.
  • db-scheduler-spring-boot3-starter # Keep same artifactId (e.g. db-scheduler-spring-boot-starter)
  • db-scheduler-spring-boot4-starter # New artifactId (e.g. db-scheduler-spring-boot4-starter)

Rationale:
The idea is to move all common classes used by both Spring Boot 3 and Spring Boot 4 into the db-scheduler-spring-common module.
Each version-specific module (spring-boot3 and spring-boot4) would only contain code that differs between the two versions.
This structure aims to:

• Avoid code duplication
• Simplify maintenance by isolating version-specific logic
• Make future upgrades easier ode that differs between the two versions.

What do you think? If you like this idea, I will start with the implementation next week.

[kagkarlsson]

This is inline with my hopes for this upgrade 🙏 👍