Generate changelog for submodules

[bachp]

Is your feature request related to a problem? Please describe.
If my repository contains submodules and I have commits updating the submodule, I only see the a commit doing the update.
The information what changed in the submodule is not visible.

If the submodule also follow the same commit convention I would like to have a way to also include the submodule commits in my changelog.

Describe the solution you'd like

Add an option to recurse into submodules.
With this option enabled, git-cliff would, whenever it encounters a commit changing a submodule revision, recurse into this submodule.
It would then get the list of all commits included in this version change and include them in the current changelog. Maybe separated by submodule to allow nicely group them in the output.

Describe alternatives you've considered

• Implement this behaviour in an external script and merge the generated MRs
• Use subtrees instead of submodules

Additional context

[snaeil]

I don't know if it's possible but it would be awesome to be able to use git-cliff as @bachp described for git subtree merging.

Example for subtree merging can be found here.