Created generic configuration framework to be used by all NFs

Code Changes

• Created generic configuration framework where configuration values are stored in an unordered_map
• Defined common configuration types: String, bool (support features), local interface, local SBI interface, remote SBI interface
• Split code into NF-specific configuration and common configuration framework:
  • Set default values
  • Set mandatory values
  • Set member variables to not break old API (can be refactored further in the future)
• Create YAML parser for new types with yaml-cpp
• Read YAML file instead of libconfig

Config Changes

• Defined YAML configuration file
• Removed old configuration
• Split HTTP1 and HTTP2 interface in configuration (supports different interfaces/IPs now)
• Removed unused values:
  • Instance ID
  • PID directory
  • slice configuration

Build Changes

• Removed libconfig build requirement in build scripts and Dockerfiles

Tests

• Tested NRF registration/de-registration manually
• API tested using the CURL requests described in Wiki