BE: Bump Spring Boot to 3.5.8

[yeikel]

What changes did you make? (Give an overview)

Maintenance upgrade

https://github.com/spring-projects/spring-boot/releases/tag/v3.5.8

How Has This Been Tested? (put an "x" (case-sensitive!) next to an item)

• Unit checks
• Integration checks
• Covered by existing automation

Checklist (put an "x" (case-sensitive!) next to all the items, otherwise the build will fail)

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (e.g. ENVIRONMENT VARIABLES)
• My changes generate no new warnings (e.g. Sonar is happy)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged

Check out Contributing and Code of Conduct

A picture of a cute animal (not mandatory but encouraged)

[yeikel]

@Haarolean @germanosin Please check this out when capacity permits 🙏