feat: add risingwave.py in db engine specs (#22123)

docs/docs/databases/risingwave.mdx

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+---
+title: RisingWave
+hide_title: true
+sidebar_position: 16
+version: 1
+---
+
+## RisingWave
+
+The recommended connector library for RisingWave is
+[sqlalchemy-risingwave](https://github.com/risingwavelabs/sqlalchemy-risingwave).
+
+The expected connection string is formatted as follows:
+
+```
+risingwave://root@{hostname}:{port}/{database}?sslmode=disable
+```

superset/db_engine_specs/risingwave.py

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+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+from superset.db_engine_specs.postgres import PostgresEngineSpec
+
+
+class RisingWaveDbEngineSpec(PostgresEngineSpec):
+    engine = "risingwave"
+    engine_name = "RisingWave"
+    default_driver = ""