feat(projections): resource counters (#9979)

# Which Problems Are Solved

Add the ability to keep track of the current counts of projection
resources. We want to prevent calling `SELECT COUNT(*)` on tables, as
that forces a full scan and sudden spikes of DB resource uses.

# How the Problems Are Solved

- A resource_counts table is added
- Triggers that increment and decrement the counted values on inserts
and deletes
- Triggers that delete all counts of a table when the source table is
TRUNCATEd. This is not in the business logic, but prevents wrong counts
in case someone want to force a re-projection.
- Triggers that delete all counts if the parent resource is deleted
- Script to pre-populate the resource_counts table when a new source
table is added.

The triggers are reusable for any type of resource, in case we choose to
add more in the future.
Counts are aggregated by a given parent. Currently only `instance` and
`organization` are defined as possible parent. This can later be
extended to other types, such as `project`, should the need arise.

I deliberately chose to use `parent_id` to distinguish from the
de-factor `resource_owner` which is usually an organization ID. For
example:

- For users the parent is an organization and the `parent_id` matches
`resource_owner`.
- For organizations the parent is an instance, but the `resource_owner`
is the `org_id`. In this case the `parent_id` is the `instance_id`.
- Applications would have a similar problem, where the parent is a
project, but the `resource_owner` is the `org_id`


# Additional Context

Closes https://github.com/zitadel/zitadel/issues/9957

cmd/setup/57.sql

@@ -0,0 +1,106 @@
+CREATE TABLE IF NOT EXISTS projections.resource_counts
+(
+    id SERIAL PRIMARY KEY, -- allows for easy pagination
+    instance_id TEXT NOT NULL,
+    table_name TEXT NOT NULL, -- needed for trigger matching, not in reports
+    parent_type TEXT NOT NULL,
+    parent_id TEXT NOT NULL,
+    resource_name TEXT NOT NULL, -- friendly name for reporting
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT now(),
+    amount INTEGER NOT NULL DEFAULT 1 CHECK (amount >= 0),
+    
+	UNIQUE (instance_id, parent_type, parent_id, table_name)
+);
+
+-- count_resource is a trigger function which increases or decreases the count of a resource.
+-- When creating the trigger the following required arguments (TG_ARGV) can be passed:
+-- 1. The type of the parent
+-- 2. The column name of the instance id
+-- 3. The column name of the owner id
+-- 4. The name of the resource
+CREATE OR REPLACE FUNCTION projections.count_resource()
+    RETURNS trigger
+    LANGUAGE 'plpgsql' VOLATILE
+AS $$
+DECLARE
+	-- trigger variables
+	tg_table_name TEXT := TG_TABLE_SCHEMA || '.' || TG_TABLE_NAME;
+	tg_parent_type TEXT := TG_ARGV[0];
+	tg_instance_id_column TEXT := TG_ARGV[1];
+	tg_parent_id_column TEXT := TG_ARGV[2];
+	tg_resource_name TEXT := TG_ARGV[3];
+	
+	tg_instance_id TEXT;
+	tg_parent_id TEXT;
+
+	select_ids TEXT := format('SELECT ($1).%I, ($1).%I', tg_instance_id_column, tg_parent_id_column);
+BEGIN
+	IF (TG_OP = 'INSERT') THEN
+		EXECUTE select_ids INTO tg_instance_id, tg_parent_id USING NEW;
+		
+		INSERT INTO projections.resource_counts(instance_id, table_name, parent_type, parent_id, resource_name)
+		VALUES (tg_instance_id, tg_table_name, tg_parent_type, tg_parent_id, tg_resource_name)	
+		ON CONFLICT (instance_id, table_name, parent_type, parent_id) DO
+		UPDATE SET updated_at = now(), amount = projections.resource_counts.amount + 1;
+		
+		RETURN NEW;
+	ELSEIF (TG_OP = 'DELETE') THEN
+		EXECUTE select_ids INTO tg_instance_id, tg_parent_id USING OLD;
+
+		UPDATE projections.resource_counts
+		SET updated_at = now(), amount = amount - 1
+		WHERE instance_id = tg_instance_id
+			AND table_name = tg_table_name
+			AND parent_type = tg_parent_type
+			AND parent_id = tg_parent_id
+			AND resource_name = tg_resource_name 
+			AND amount > 0; -- prevent check failure on negative amount.
+		
+		RETURN OLD;
+	END IF;
+END
+$$;
+
+-- delete_table_counts removes all resource counts for a TRUNCATED table.
+CREATE OR REPLACE FUNCTION projections.delete_table_counts()
+	RETURNS trigger
+	LANGUAGE 'plpgsql'
+AS $$
+DECLARE
+	-- trigger variables
+	tg_table_name TEXT := TG_TABLE_SCHEMA || '.' || TG_TABLE_NAME;
+BEGIN
+	DELETE FROM projections.resource_counts
+	WHERE table_name = tg_table_name;
+END
+$$;
+
+-- delete_parent_counts removes all resource counts for a deleted parent.
+-- 1. The type of the parent
+-- 2. The column name of the instance id
+-- 3. The column name of the owner id
+CREATE OR REPLACE FUNCTION projections.delete_parent_counts()
+	RETURNS trigger
+	LANGUAGE 'plpgsql'
+AS $$
+DECLARE
+	-- trigger variables
+	tg_parent_type TEXT := TG_ARGV[0];
+	tg_instance_id_column TEXT := TG_ARGV[1];
+	tg_parent_id_column TEXT := TG_ARGV[2];
+	
+	tg_instance_id TEXT;
+	tg_parent_id TEXT;
+
+	select_ids TEXT := format('SELECT ($1).%I, ($1).%I', tg_instance_id_column, tg_parent_id_column);
+BEGIN
+	EXECUTE select_ids INTO tg_instance_id, tg_parent_id USING OLD;
+	
+	DELETE FROM projections.resource_counts
+		WHERE instance_id = tg_instance_id
+		AND parent_type = tg_parent_type
+		AND parent_id = tg_parent_id;
+	
+	RETURN OLD;
+END
+$$;