Add dashboard for redis keys (#9746)

Add a dashboard with details for Redis keys using the new key metricset.
Visualizations included show lists length, what is useful when redis is used
for queuing, and average strings sizes and TTLs, what is useful when Redis
is used as a cache.

CHANGELOG.asciidoc

@@ -80,6 +80,8 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 
 *Metricbeat*
 
+- Add `key` metricset to the Redis module. {issue}9582[9582] {pull}9657[9657] {pull}9746[9746]
+
 *Packetbeat*
 
 *Functionbeat*
@@ -231,7 +233,6 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha1...v7.0.0-alpha2[Check the
 - Support GET requests in Jolokia module. {issue}8566[8566] {pull}9226[9226]
 - Add freebsd support for the uptime metricset. {pull}9413[9413]
 - Add `host.os.name` field to add_host_metadata processor. {issue}8948[8948] {pull}9405[9405]
-- Add `key` metricset to the Redis module. {issue}9582[9582] {pull}9657[9657]
 - Add more TCP statuses to `socket_summary` metricset. {pull}9430[9430]
 - Remove experimental tag from ceph metricsets. {pull}9708[9708]
 

metricbeat/docs/fields.asciidoc

@@ -20326,6 +20326,16 @@ type: keyword
 Key name.
 
 
+--
+
+*`redis.key.id`*::
++
+--
+type: keyword
+
+Unique id for this key (With the form <keyspace>:<name>).
+
+
 --
 
 *`redis.key.type`*::