feature: /config shows the router's PostgreSQL clusters and their settings, and /postgresql their databases with their sizes.

README.md

@@ -666,6 +666,16 @@ curl -H "Authorization: Bearer $TOKEN" http://10.0.0.4:7081/config
 | `ipsec` | `connections` and `sas`: one object per connection and per IKE SA, read from `swanctl --list-conns --pretty` and `swanctl --list-sas --pretty`, with the connection's name under `name` and swanctl's keys and string values |
 | `wireguard` | The public key and port of `wg0`, and each peer's public key, endpoint, allowed IPs, handshake age and traffic; no private or preshared key |
 | `docker` | `docker.exposed_ports` and the rules of the `VPN-ROUTER-DOCKER` chain |
+| `postgresql` | `clusters`: each PostgreSQL cluster of `pg_lsclusters` with its version, name, port, status and data directory, and for one that is online its `settings`: `server_version`, `listen_addresses`, `port`, `max_connections`, `shared_buffers`, `effective_cache_size`, `work_mem`, `password_encryption`, `ssl` and `timezone`; `null` when `pg_lsclusters` fails |
+
+### The /postgresql page
+
+`/postgresql`, with the same token as `/config`, shows the databases of the PostgreSQL clusters on the
+router:
+
+- **Content:** `clusters` lists each cluster with its version, name, port and status, its `databases` (name, owner, encoding and size in bytes, `pg_database_size`) and their total `size`.
+- **A cluster that is not online:** `databases` and `size` are `null`.
+- **Collection:** the web service reads it with `psql` as the `postgres` user at each request.
 
 ### The /users API