Replace wrapper.vm in productivity_analytics/filter_dropdowns_spec

What does this MR do and why?

Issue: #391141 (closed)

• Set state.groupNamespace as the default value during init
• Replace wrapper.vm.groupId with createWrapper({ group: { id: groupId } })
• Replace wrapper.vm.onGroupSelected(...) with findGroupsDropdownFilter().vm.$emit('selected', ...)
• Replace wrapper.vm.onProjectsSelected(...) with findProjectsDropdownFilter().vm.$emit('selected', ...)

How to set up and validate locally

yarn jest ee/spec/frontend/analytics/productivity_analytics/components/filter_dropdowns_spec.js

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.