Create a graphql query to return the projects that are associated to policy_scope
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## Why are we doing this work
While working on https://gitlab.com/groups/gitlab-org/-/epics/5510+ we identified that the count of projects we show for a security policy that is linked to a compliance framework is not the exact count. Currently we show the count of all projects in the root-level group that has the compliance framework linked, but if the policy is linked to a sub-group, we need to show the count of projects within the sub-group rather than the root group.
As a part of this issue, we want to introduce a graphql API to return the count of projects that are associated with the scope (`policy_scope`) of the policy.
## Relevant links
- Related discussion: https://gitlab.com/gitlab-org/gitlab/-/issues/432513#note_1843748027
## Non-functional requirements
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