Group PRs by module in the changelog

[mrcasals]

When generating the changelog using #7461, we get the list of PRs sorted by type of change:

• Added
• Changed
• Fixed
• Removed
• Developer improvements

But it's a bit difficult to find what changes affect a given module. The current output follows this structure:

### Added

- **decidim-core**, **decidim-admin**: Blah blah #1234
- **decidim-proposals**: Blah #2345
- Blah blah #7654

### Changed
...

We could reorganize the output to group the PRs by type of change and module:

### Added

#### decidim-core

- Blah blah #1234

#### decidim-admin

- Blah blah #1234

#### decidim-proposals

- Blah #2345

### Other

- Blah blah #7654

### Changed
...

Notice how the reference to #1234 is duplicated because it affects two different modules.

It's more verbose than the curren version, but I think this would help on the readability of the changelog.

[andreslucena]

I agree with this one!! 👏🏽 👏🏽

Although this would mean diverging from a standard (our format comes from https://keepachangelog.com/), I think that we should be migrating to a better separation of the different modules and this is a nice step in that direction. For instance, there are cases where installations are only using a couple of modules (like decidim-initiatives, see https://petitions.senat.fr/) and it don't make sense to have to scan for this module only.

[andreslucena]

After some months without seeing this proposal, I like it even more 😄

This is also how Rails orders its releases notes: https://edgeguides.rubyonrails.org/7_0_release_notes.html

[andreslucena]

Moving this to a discussion so it gets more visibility

[paulinebessoles]

I just discovered this discussion, and totally agree that this would improve changelog readability a lot, also for for non-developers! 😁