CAMEL-23213: Handle Spring Boot catalog provider requiring JDK 21+

[gnodet]

Summary

• CatalogLoader.loadSpringBootCatalog() now catches UnsupportedClassVersionError when loading SpringBootRuntimeProvider and provides a clear error message: "Spring Boot runtime requires JDK 21+ starting from camel-spring-boot 4.19.0. Use --camel-spring-boot-version=4.18.x for JDK 17 compatibility, or run on JDK 21+."
• Tests (ExportTest, ExportMainApplicationProperties, DependencyListTest, DependencyUpdateTest) skip Spring Boot runtime type on JDK < 21

Context

camel-spring-boot 4.19.0-SNAPSHOT moved to Spring Boot 4 (JDK 21). The camel-catalog-provider-springboot artifact is now compiled with Java 21 bytecode (class file version 65.0), causing UnsupportedClassVersionError on JDK 17. This broke camel jbang export --runtime=spring-boot on JDK 17 and caused CI failures on JDK 17 for any PR whose incremental build pulled in camel-jbang-core.

Note: reverting the camel-spring-boot catalog to compile with JDK 17 would not help, since Spring Boot 4 itself requires JDK 21 — users on JDK 17 cannot run Spring Boot 4 applications anyway. The right approach is to guide them to use --camel-spring-boot-version=4.18.x (which targets Spring Boot 3.x / JDK 17) or upgrade to JDK 21+.

Test plan

• All 75 tests pass on JDK 21+ (Spring Boot tests included)
• CI validates JDK 17 no longer fails (Spring Boot tests skipped)

[github-actions]

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[github-actions]

🧪 CI tested the following changed modules:

• dsl/camel-jbang/camel-jbang-core

Full reactor (26 modules)

• Camel :: Coverage
• Camel :: Coverage [pom]
• Camel :: JBang :: Core
• Camel :: JBang :: Core [jar]
• Camel :: JBang :: Integration tests
• Camel :: JBang :: Integration tests [jar]
• Camel :: JBang :: MCP
• Camel :: JBang :: MCP [jar]
• Camel :: JBang :: Main
• Camel :: JBang :: Main [jar]
• Camel :: JBang :: Plugin :: Edit
• Camel :: JBang :: Plugin :: Edit [jar]
• Camel :: JBang :: Plugin :: Generate
• Camel :: JBang :: Plugin :: Generate [jar]
• Camel :: JBang :: Plugin :: Kubernetes
• Camel :: JBang :: Plugin :: Kubernetes [jar]
• Camel :: JBang :: Plugin :: Route Parser
• Camel :: JBang :: Plugin :: Route Parser [jar]
• Camel :: JBang :: Plugin :: Testing
• Camel :: JBang :: Plugin :: Testing [jar]
• Camel :: JBang :: Plugin :: Validate
• Camel :: JBang :: Plugin :: Validate [jar]
• Camel :: Launcher
• Camel :: Launcher [jar]
• Camel :: Launcher :: Container
• Camel :: Launcher :: Container [pom]