SpringBoot Refactor RSocketPortInfoApplicationContextInitializer to extract "server.ports" to a constant

This commit refactors the RSocketPortInfoApplicationContextInitializer class to replace the hardcoding of "server.ports" with a constant named SERVER_PORTS. This improves code maintainability and readability.

• Introduced a constant for "server.ports"
• Updated all references to use the constant

Comment From: mhalbritter

Thank you very much and congratulations on your first contribution :tada:!

Comment From: ch4570

Thank you for accepting my Pull Request. We will contribute more in the future. Have a goodday!