Add backend changes to allow hard deleting orgs on Cloud
Created by: miveronese
Ticket: https://sourcegraph.atlassian.net/browse/CLOUD-81
This PR adds the backend changes that allow org members, when on Cloud, hard deleting an org they belong to. In a previous merged PR, an integration test failed during the CI build.. That PR was reverted, the issue was fixed (here is the commit with the fix) and this new PR is now open.
Test plan
To run an integration test that previously failed during the CI build:
go test -long -base-url "https://sourcegraph.test:3443" -email <email> -username <username> -password <password> -run TestSiteAdminEndpoints -v
To run unit tests added/updated:
go test ./cmd/frontend/graphqlbackend/. -v -run TestRemoveOrganization
go test ./internal/database/. -run TestDeleteOrganization_OnPremise -v
go test ./internal/database/. -run TestDeleteOrganization_OnCloud -v
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