Disable accountability automated progress caluclations

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

Currently the accountability module calculates the progress percentage of the parent project when a child project is updated. The percentage is calculated according to this functionality:

https://github.com/decidim/decidim/blob/5f382c71d9a96fe2c5599024957cf91ba0f80c40/decidim-accountability/app/models/decidim/accountability/result.rb#L54-L58

This is not always desired. Sometimes the content managers want to keep a separate progress percentage on the "parent" project and separate progress on all of its children.

An example situation is a case where you have main project that has been updated regularly until a point. After this point, a new child project is added which will have 0% progress when it starts. Now in this situation, the parent progress should still be 25%, although the child progress is 0% for the only child.

**Describe the solution you'd like**

I'd like to have an extra configuration on the accountability component that would allow disabling the automatic progress calculation for the parent projects.

**Describe alternatives you've considered**

Currently it is possible to accomplish this from the UI but it is a bit clunky. After every time the content managers will update the sub-project, they will have to remember to go to the parent project editing view and update its progress back to the original value.

This is, however, a bit complicated and not very intuitive.

**Additional context**

N/A

**Does this issue could impact on users private data?**

No.

**Funded by**

So far only reported.