Add Spring Boot 4.0 support with working samples

[tobixlea]

Issue #, if available:

Description of changes:

• Add aws-serverless-java-container-springboot4 module with Spring Framework 7.x support
• Add aws-serverless-springboot4-archetype for project generation
• Add 4 working Spring Boot 4.0 samples:
  • Basic pet-store: compatible and tested with java25 runtime
  • alt-pet-store: compatible and tested with java25 runtime
  • graphql-pet-store: compatible and tested with java25 runtime
  • pet-store-native: compatible and tested with java25 runtime
• All samples tested and deployed successfully to AWS Lambda
• Full compatibility with Jakarta EE 11 and Java 21 runtime
• Update root pom.xml to include new modules"
• removal of ${project.version} variable in archetype pom files in favor of explicit versioning

By submitting this pull request

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I confirm that I've made a best effort attempt to update all relevant documentation.

[bnusunny]

Looks good overall. Please check the two comments I left.

[valerena]

I don't know how this worked, but if it was this sort of variable ${project.version} we might want to keep it like that, so it's easier in the future to update? (unless there's a reason to not do it, and it should be mentioned in the PR description)

(same in other pom.xml files).