Update Code documentation for new CLI commands and add "help" command to assist user

https://github.com/ArduPilot/MissionPlanner/blob/eccdc1c9276e05a18056aecf2c798ce8e0fc6fb2/MainV2.cs#L3046

This code doc is old, the CLI handles many more inputs now. Update the code documentation.

Additionally, add a "help" command which displays the available CLI for the user.

Start in MainV2.cs around line 3046 and inspect how the CLI currently parses and documents its inputs. Update the code documentation to cover the existing commands, then add a help command that displays the available CLI options. Verify the documented commands and help output through the CLI entry point.

Written by the indexing model from the issue text.