Handle F1 Reset at DU, and ensure state re-init on F1Setup

This MR implements the following:

1. F1AP Reset:
   • Initializes the stubs for F1 Reset, both CU and DU.
   • Implementation for F1 Reset handling at the DU, both encoder/ decoder, and handlers.
2. F1SetupRequest:
   • Ensure the UE-related states are always cleared on every F1SetupRequest (especially when DU re-establishes its SCTP connection with the CU).
     • Quoted from TS38.473 8.2.3.2, "This procedure erases any existing application level configuration data in the two nodes and replaces it with the one received. This procedure also re-initializes the F1AP UE-related contexts (if any) and erases all related signaling connections in the two nodes like a Reset procedure would do."
     • Impact: Restarting the CU midway will not result in a crash.

Both (1) and (2) use similar logic in re-init/initializing the UE-related states in the DU, i.e., clear MAC/RLC, F1, and GTP.

HOWEVER, I am not 100% sure whether my interpretation of the standards is correct for the above, i.e., Reset and F1Setup.

So, feedback and discussions are welcome. Thanks!

Important notes:

• F1Reset handling at the DU is currently limited to the entire "f1-Interface", i.e., all states are cleared, "partialF1-interface" still needs to be looked further into which may come in a separate MR later.
• F1Reset handling is not implemented at the CU; neither CU nor DU currently generates/sends out the F1Reset.
• F1Reset handling at the DU is tested using an SCTP proxy in F1-C that generates the F1 Reset messages.