[Maintenance] Leverage Spring 3.5 Features

[devtobi]

Relevant component

refarch-gateway, refarch-integrations, refarch-tools

Problem description (optional)

No response

Desired solution

Spring Boot 3.5.0 got some new exciting features we could investigate to simplify some things and get rid of boilerplate code, e.g.:

• Registering of Filters and Servlets via Annotations (useful for custom filter classes)
• Loading multiple properties via single environment variable
• Improvements in OAuth2 Auto-Configuration
• Improvements for Cloud Native Buildpacks -> Why do we build our image via Dockerfile instead via Springs Buildpack feature?

Some other stuff from miscellaneous:

• A new @ConditionalOnBooleanProperty annotation has been introduced

Keep is mind this issue also affects https://github.com/it-at-m/refarch-templates

Considered alternatives (optional)

No response

Additional context (optional)

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