Add AccessPointAttributes JSON serialization/deserialization support

[abeltrano]

Type

• Bug fix
• Feature addition
• Feature update
• Documentation
• Build Infrastructure

Side Effects

• Breaking change
• Non-functional change

Goals

• Allow AccessPointAttributes to be encoded as JSON.
• Allow AccessPointAttributes to be instantiated with JSON input (std::string, std::ifstream (intended for file)).

Technical Details

• Add nlohmann::json to/from parsers for AccessPointAttributes.
• Add basic unit test.

Test Results

• All unit tests pass.

Reviewer Focus

• None

Future Work

• Allow specifying JSON file on command-line for netremote-server.

Checklist

• Build target all compiles cleanly.
• clang-format and clang-tidy deltas produced no new output.
• Newly added functions include doxygen-style comment block.