DB timeout querying for LOW vulnerabilities

This report is currently timing-out: https://gitlab.com/gitlab-org/gitlab/-/security/vulnerability_report/?severity=LOW

https://sentry.gitlab.net/gitlab/gitlabcom/issues/2599792/?referrer=gitlab_plugin

PG::QueryCanceled: ERROR:  canceling statement due to statement timeout

  active_record/connection_adapters/postgresql_adapter.rb:675:in `exec_params'
    @connection.exec_params(sql, type_casted_binds)
  graphql/types/relay/base_connection.rb:107:in `nodes'
    @object.edge_nodes
  graphql/schema/field.rb:692:in `public_send'
    obj.public_send(@resolver_method)
  graphql/schema/field.rb:692:in `block in public_send_field'
    obj.public_send(@resolver_method)
  graphql/schema/field.rb:733:in `block in with_extensions'
    yield(obj, args)
...
(245 additional frame(s) were not displayed)

ActiveRecord::QueryCanceled: PG::QueryCanceled: ERROR:  canceling statement due to statement timeout

Implementation plan

• Use new vulnerability_reads model to speed up the query, blocked by #335503 (closed)