fix: Reconcile on SubscriptionManager init

[edgurgel]

What kind of change does this PR introduce?

Instead of always deleting the subscriptions table when SubscriptionManager starts we:

• Cold start cleans up the DB
• Warm restarts now re-adopt ETS and re-monitor subscribers

Orphan processes are not a problem because ReplicationPoller simply broadcasts if it can't find the pid/node related to the subscription row. See

realtime/lib/extensions/postgres_cdc_rls/replication_poller.ex

Lines 251 to 273 in ca0a9bc

	case collect_subscription_nodes(subscribers_nodes_table, change.subscription_ids) do
	{:ok, nodes} ->
	for {node, subscription_ids} <- nodes do
	TenantBroadcaster.pubsub_direct_broadcast(
	node,
	tenant_id,
	topic,
	# Send only the subscription IDs relevant to this node
	{change.type, payload, MapSet.new(subscription_ids)},
	MessageDispatcher,
	:postgres_changes
	)
	end
	{:error, :node_not_found} ->
	TenantBroadcaster.pubsub_broadcast(
	tenant_id,
	topic,
	{change.type, payload, change.subscription_ids},
	MessageDispatcher,
	:postgres_changes
	)
	end

One option that I decided to not implement was to do a "delete from subscription NOT IN $alive_sub_ids" as this can be problematic depending on the size of the table and it's not a huge issue to have orphan rows there momentarily. It's also more complicated.

[coveralls]

Coverage is 91.533% — fix/subscription-manager-reconciliation into main. No base build found for main.

[realtime-release-bot]

🎉 This PR is included in version 2.107.5 🎉

The release is available on GitHub release

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