Send notification when initiative reaches 100% of support thereshold

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

We currently have notifications for milestones (25%, 50%, 75%) leading to the support threshold but none for when the notification reaches the support threshold.

**Describe the solution you'd like**

I'd like : authors, promoting committee members, followers of the initiative and admins to receive a notification when an initiative reaches the support threshold.

**Describe alternatives you've considered**

Setting a milestone to 100%. Not sure if it'd work. **Additional context**

The PR is here

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

No

**Funded by**

OSP