Add cardinality tips to FAQ and sqlserver input (#6852)

plugins/inputs/sqlserver/README.md

@@ -109,7 +109,14 @@ The new (version 2) metrics provide:
 - *Server properties*: Number of databases in all possible states (online, offline, suspect, etc.), cpu count, physical memory, SQL Server service uptime, and SQL Server version. In the case of Azure SQL relevent properties such as Tier, #Vcores, Memory etc.
 - *Wait stats*: Wait time in ms, number of waiting tasks, resource wait time, signal wait time, max wait time in ms, wait type, and wait category. The waits are categorized using the same categories used in Query Store.
 - *Schedulers* - This captures sys.dm_os_schedulers.
-- *SqlRequests* - This captures a snapshot of dm_exec_requests and dm_exec_sessions that gives you running requests as well as wait types and blocking sessions
+- *SqlRequests* - This captures a snapshot of dm_exec_requests and
+  dm_exec_sessions that gives you running requests as well as wait types and
+  blocking sessions.
+
+  In order to allow tracking on a per statement basis this query produces a
+  unique tag for each query.  Depending on the database workload, this may
+  result in a high cardinality series.  Reference the FAQ for tips on
+  [managing series cardinality][cardinality].
 - *Azure Managed Instances*
   - Stats from `sys.server_resource_stats`:
     - cpu_count
@@ -165,3 +172,5 @@ The following metrics can be used directly, with no delta calculations:
 Version 2 queries have the following tags:
 - `sql_instance`: Physical host and instance name (hostname:instance)
 - database_name:  For Azure SQLDB, database_name denotes the name of the Azure SQL Database as server name is a logical construct.
+
+[cardinality]: /docs/FAQ.md#user-content-q-how-can-i-manage-series-cardinality