添加 mysql redis postgres 插件

plugins/postgres/docs/create.md

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+Official Postgres "$DOCKER_BIN" image ls does not include postgis extension (amongst others). The following example creates a new postgres service using `postgis/postgis:13-3.1` image, which includes the `postgis` extension.
+
+```shell
+# use the appropriate image-version for your use-case
+dokku postgres:create postgis-database --image "postgis/postgis" --image-version "13-3.1"
+```
+
+To use pgvector instead, run the following:
+
+```shell
+# use the appropriate image-version for your use-case
+dokku postgres:create pgvector-database --image "pgvector/pgvector" --image-version "pg17"
+```