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

internal/migration/count_trigger.sql

@@ -0,0 +1,43 @@
+{{ define "count_trigger" -}}
+CREATE OR REPLACE TRIGGER count_{{ .Resource }}
+    AFTER INSERT OR DELETE
+    ON {{ .Table }}
+    FOR EACH ROW
+    EXECUTE FUNCTION projections.count_resource(
+        '{{ .ParentType }}', 
+        '{{ .InstanceIDColumn }}', 
+        '{{ .ParentIDColumn }}',
+        '{{ .Resource }}'
+    );
+
+CREATE OR REPLACE TRIGGER truncate_{{ .Resource }}_counts
+    AFTER TRUNCATE
+    ON {{ .Table }}
+    FOR EACH STATEMENT
+    EXECUTE FUNCTION projections.delete_table_counts();
+
+-- Prevent inserts and deletes while we populate the counts.
+LOCK TABLE {{ .Table }} IN SHARE MODE;
+
+-- Populate the resource counts for the existing data in the table.
+INSERT INTO projections.resource_counts(
+	instance_id,
+    table_name,
+    parent_type,
+    parent_id,
+    resource_name,
+    amount
+)
+SELECT
+    {{ .InstanceIDColumn }},
+    '{{ .Table }}',
+    '{{ .ParentType }}',
+    {{ .ParentIDColumn }},
+    '{{ .Resource }}',
+    COUNT(*) AS amount
+FROM {{ .Table }}
+GROUP BY ({{ .InstanceIDColumn }}, {{ .ParentIDColumn }})
+ON CONFLICT (instance_id, table_name, parent_type, parent_id) DO
+UPDATE SET updated_at = now(), amount = EXCLUDED.amount;
+
+{{- end -}}