Allow all members of a group to edit a proposal submitted by their group

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

Currently proposals that are submitted on behalf of a group are only editable by the one account that submitted them.

Describe the solution you'd like

Any account that is a member of a group should be able to edit the proposals submitted by a group they belong to.

Describe alternatives you've considered

Potentially make this behaviour optional from the back office - adding a checkbox in the group settings.

Funded by
No funding, but we are very open for cofinancing. We think the group feature is underutilized and could beenfit from improvements like this.