feat: Add title to top of the parts of the files if using the --split command

[catmo-syntasso]

Currently if a user runs the --split command, the files generated are either:

1. empty; or
2. a direct copy of the part of the promise they represent.

To make it easier for a user to understand, and to perhaps make it easier for a tool to parse, we should add a line to the top of the yaml.

This should be true for all parts generated by the --split command which AFAIK is dependencies, api, and workflows