Base Libraries: Update Spring Boot to v3.5.4

[tangobravo62]

Since most prosEO environments have now been migrated to a current Linux kernel, we can now start the long overdue migration from Spring Boot 2.x to 3.x. At the time of this writing, Spring Boot 3.5.4 is the current version, so this shall be the new baseline.

This issue contains the following sub-tasks:

• Gap analysis and specification of necessary changes for the migration from Spring Boot 2.7.18 to Spring Boot 3.5.4
  (see also Mind the Gap: Jumping from Spring Boot 2.x to 3.x)
• Migration of the prosEO VAL environment in the IONOS Cloud from CentOS 7 to Rocky Linux 9
• Update of all prosEO kernel components (including Base Libraries: Change base image to Eclipse Temurin #194 )
• Migration of the prosEO GUI to Bootstrap 5

Precondition for this issue is the release of prosEO 1.2.0 (GUI changes to implement with first priority as per #218 ).

[tangobravo62]

First successful run with unit tests and regression test, see attached screenshot.