PG-2312 - Reorganize Docker installation instructions (#957)

This PR updates and reorganizes the instructions and content in docker.md for easier flow and user readability.

Author: Andriciuc

docs/docker.md

@@ -0,0 +1,98 @@
+# Enable `pg_stat_monitor` for performance statistics
+
+`pg_stat_monitor` is a query performance monitoring tool for PostgreSQL which aggregates collected performance statistics.
+
+For more information on this extension, see [pg_stat_monitor :octicons-link-external-16:](https://docs.percona.com/pg-stat-monitor/).
+
+## Enable pg_stat_monitor {.power-number}
+
+1. Start the container as shown in [Run in Docker](docker.md#start-container), adding the following option to the `docker run` command:
+
+    ```{.bash data-prompt="$"}
+    -c shared_preload_libraries=pg_stat_monitor
+    ```
+
+2. Connect to the container and start the interactive `psql` session:
+
+    ```{.bash data-prompt="$"}
+    docker exec -it container-name psql -U postgres
+    ```
+
+    ??? example "Sample output"
+
+        ```{.text .no-copy}
+        psql ({{pgsubversion}} - Percona Server for PostgreSQL {{dockertag}})
+        Type "help" for help.
+
+        postgres=#
+        ```
+
+3. Create the extension in the desired database:
+
+    ```sql
+    CREATE EXTENSION pg_stat_monitor;
+    ```
+
+    ??? example "Sample output"
+
+            ```{.text .no-copy}
+            postgres=# CREATE EXTENSION pg_stat_monitor;
+            CREATE EXTENSION
+            ```
+
+4. Verify the setup:
+
+    ```sql
+    \d pg_stat_monitor;
+    ```
+
+??? example "Output"
+
+    ```
+                             View "public.pg_stat_monitor"
+          Column        |           Type           | Collation | Nullable | Default
+    ---------------------+--------------------------+-----------+----------+---------
+    bucket              | integer                  |           |          |
+    bucket_start_time   | timestamp with time zone |           |          |
+    userid              | oid                      |           |          |
+    dbid                | oid                      |           |          |
+    queryid             | text                     |           |          |
+    query               | text                     |           |          |
+    plan_calls          | bigint                   |           |          |
+    plan_total_time     | numeric                  |           |          |
+    plan_min_timei      | numeric                  |           |          |
+    plan_max_time       | numeric                  |           |          |
+    plan_mean_time      | numeric                  |           |          |
+    plan_stddev_time    | numeric                  |           |          |
+    plan_rows           | bigint                   |           |          |
+    calls               | bigint                   |           |          |
+    total_time          | numeric                  |           |          |
+    min_time            | numeric                  |           |          |
+    max_time            | numeric                  |           |          |
+    mean_time           | numeric                  |           |          |
+    stddev_time         | numeric                  |           |          |
+    rows                | bigint                   |           |          |
+    shared_blks_hit     | bigint                   |           |          |
+    shared_blks_read    | bigint                   |           |          |
+    shared_blks_dirtied | bigint                   |           |          |
+    shared_blks_written | bigint                   |           |          |
+    local_blks_hit      | bigint                   |           |          |
+    local_blks_read     | bigint                   |           |          |
+    local_blks_dirtied  | bigint                   |           |          |
+    local_blks_written  | bigint                   |           |          |
+    temp_blks_read      | bigint                   |           |          |
+    temp_blks_written   | bigint                   |           |          |
+    blk_read_time       | double precision         |           |          |
+    blk_write_time      | double precision         |           |          |
+    host                | bigint                   |           |          |
+    client_ip           | inet                     |           |          |
+    resp_calls          | text[]                   |           |          |
+    cpu_user_time       | double precision         |           |          |
+    cpu_sys_time        | double precision         |           |          |
+    tables_names        | text[]                   |           |          |
+    wait_event          | text                     |           |          |
+    wait_event_type     | text                     |           |          |
+    ```
+
+!!! note
+     The `pg_stat_monitor` view is available only for the databases where you enabled it. If you create a new database, make sure to create the view for it to see its statistics data.