examples: add a postgres replication example using CDC

Note that we can't dynamically do anything with the schema at the
moment, we don't emit schema changes and creating the migration
statements would require a complicated sql_raw output.

config/examples/cdc_replication.yaml

@@ -0,0 +1,54 @@
+input:
+  postgres_cdc:
+    dsn: postgres://me:foobar@localhost:5432?sslmode=disable
+    include_transaction_markers: true
+    slot_name: test_slot_native_decoder
+    stream_snapshot: true
+    schema: public
+    tables: [my_src_table]
+    # Group by transaction, each message batch is all rows changed in a transaction
+    # this might be massive, but might be required for foreign key constraints
+    batching:
+      check: '@operation == "commit"'
+      period: 10s
+      processors:
+        # But drop the placeholder messages for start/end transaction
+        - mapping: |
+            root = if @operation == "begin" || @operation == "commit" {
+              deleted()
+            } else {
+              this
+            }
+output:
+  # Dispatch the write based on the operation metadata
+  switch:
+    strict_mode: true
+    cases:
+      - check: '@operation == "read" || @operation == "insert"'
+        output:
+          sql_insert:
+            driver: postgres
+            dsn: postgres://me:foobar@localhost:5432?sslmode=disable
+            table: my_dst_table
+            columns: [id, foo, bar]
+            args_mapping: root = [this.id, this.foo, this.bar]
+            init_statement: |
+              CREATE TABLE IF NOT EXISTS my_dst_table (
+                id serial PRIMARY KEY,
+                foo text,
+                bar timestamp
+              );
+      - check: '@operation == "update"'
+        output:
+          sql_raw:
+            driver: postgres
+            dsn: postgres://me:foobar@localhost:5432?sslmode=disable
+            query: UPDATE my_dst_table SET foo = $1, bar = $2 WHERE id = $3
+            args_mapping: root = [this.foo, this.bar, this.id]
+      - check: '@operation == "delete"'
+        output:
+          sql_raw:
+            driver: postgres
+            dsn: postgres://me:foobar@localhost:5432?sslmode=disable
+            query: DELETE FROM my_dst_table WHERE id = $1
+            args_mapping: root = [this.id]