Implements the validation of subscription identifier properties in SUBSCRIBE

Release notes

Created model class for subscription identifier and implemented decode and verification in SUBSCRIBE

[x] My code follows the style guidelines of this project
[x] I have commented my code, particularly in hard-to-understand areas
~~[ ] I have made corresponding changes to the documentation~~
~~[ ] I have made corresponding change to the default configuration files (and/or docker env variables)~~
[x] I have added tests that prove my fix is effective or that my feature works
[x] I have updated the Changelog if it's a feature or a fix that has to be reported