Support `.json5`, `yaml`, or `toml` config files

Thanks for stopping by to let us know something could be better!

### Is your feature request related to a problem? Please describe.

JSON5 supports comments, trailing commas, and other QoL features. It would be great to be able to support these "human-centric" formats for the config files.

### Describe the solution you'd like

I'd like to be able to write `release-please-config.json` as `json5`, `yaml` or `toml` due to the QoL features those languages support.

### Describe alternatives you've considered

Maintain a separate file and generate the json file from the source. This is annoying to do...

**Additional context**
n/a