Add doc for min/max_over_time

Author: dnhatn

docs/reference/query-languages/esql/_snippets/commands/layout/ts.md

@@ -0,0 +1,28 @@
+## `TS` [esql-ts]
+
+The `TS` command is similar to the [FROM](from.md) source command,
+but with two key differences: it targets only [time-series indices](docs-content://manage-data/data-store/data-streams/time-series-data-stream-tsds.md)
+and enables the use of time-series aggregation functions
+with the [STATS](stats-by.md) command.
+
+**Syntax**
+
+```esql
+TS index_pattern [METADATA fields]
+```
+
+**Parameters**
+
+`index_pattern`
+:   A list of indices, data streams or aliases. Supports wildcards and date math.
+
+`fields`
+:   A comma-separated list of [metadata fields](/reference/query-languages/esql/esql-metadata-fields.md) to retrieve.
+
+**Examples**
+
+```esql
+TS metrics
+| STATS sum(last_over_time(memory_usage))
+```
+