Add configuration file option for changelog --start-rev/--incremental

[janw]

Description

When adopting commitizen and Conventional Commits on a long-running existing project, there are many old commits that do not follow the formatting spec. Thus running cz changelog always requires the --start-rev or --incremental parameter to be set so that it only considers commits after a certain point in time and not try to parse poorly formatted commit messages.

Possible Solution

1. Introduce a configuration flag à la changelog_incremental (defaulting to False to mimic current behavior), that when set to True would have the same effect as providing the --incremental flag.
2. Introduce a configuration flag à la changelog_start_rev that can hold a Git rev from which to always start creating the changelog.

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Again, if this is something the maintainers agree is a useful feature, I'd be happy to provide a PR for it.

[Lee-W]

Thanks for your suggestion! I like this idea!

[woile]

I'm in for this change, I like it 💪

[Lee-W]

As #294 is merged, I'll close this one. Thanks for the contribution 🙏