Feature Request: Scripts to Convert Impl Graphs to Sim Files

**Describe desired feature**

Add tooling scripts that convert graph dumps from each of the supported implementations into a simfile that can run sim-ln in simulation mode with that graph.

Args:
- Input file: path to the graph file that needs to be converted
- Output file: optional path that simfile should be written to (some sensible default if not set)

I'd see us supporting one script per LN impl, since each has different output formats.

**Use case for feature**

If you're just looking to run something on mainnet (or a reduced version of the mainnet graph), build in scripting like this will massively reduce friction to using the simulator.

I have an ugly version of this for [LND](https://github.com/carlaKC/attackathon/blob/master/setup/lnd_to_simln.py) which needs cleaning up. _Maybe_ we want this to be a bash script rather than python - open to arguments in either direction!

**Would you like to contribute code for this feature?**

No - up for grabs!