feat: extend fiveg_rfsim interface

[gatici]

Description

This PR extends the fiveg_rfsim interface according to canonical/charm-relation-interfaces#202 by putting RFSIM address, SST and SD information to the relation data bag.

• Validates Provider application data before putting the information to the relation data bag
• Removes custom events and only uses standart charm events (relation joined, relation changed) to simplify the implementation
• Expand unit tests for fiveg_rfsim interface

Dependencies

The implementation in the charm depends on fiveg_f1 interface as this interface is used to get the SST and SD data from CU charm. fiveg_rfsim relation should wait until data is retrieved through fiveg_f1 relation. #58 should be merged.

Note

fiveg_f1 interface can carry multiple PLMNs and each PLMN includes SST and SD.
Which SST and SD value should be sent to UE in the fiveg_rfsim relation data ?
After discussing this with @Gmerold , TE126 updated to use the first PLMN.
Fiveg_rfsim interface only used with UE simulator.
For real UE's, device group of slice includes the IMSI which can be associated with the related UE.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that validate the behaviour of the software
• I validated that new and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have bumped the version of the library