fix(`beacon.gen.proxy_endpoint`): configure ProxyEndpoint `:pubsub_server` #659

Job	Run time
quality: OTP 27 \| Elixir 1.18 \| Phoenix ~> 1.7 \| LV ~> 1.0	48s
test: OTP 23 \| Elixir 1.14.0 \| Phoenix 1.7.0 \| LV 0.20.2 \| PG 13.0-alpine	6m 18s
test: OTP 27 \| Elixir 1.18 \| Phoenix ~> 1.7 \| LV ~> 1.0 \| PG 16.4-alpine	4m 38s
	11m 44s

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