Add support for SQL responses in key/value format (elastic#15845)

There are some queries like mysql `SHOW STATUS` that display the
results in a key/value format so they need to be scanned in a different
way, being the key the first column of the response and the value the
second one.

(cherry picked from commit d8517c6)

CHANGELOG.next.asciidoc

@@ -181,6 +181,9 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Enable script processor. {pull}14711[14711]
 - Add mixer metricset for Istio Metricbeat module {pull}15696[15696]
 - Add mesh metricset for Istio Metricbeat module{pull}15535[15535]
+- Make the `system/cpu` metricset collect normalized CPU metrics by default. {issue}15618[15618] {pull}15729[15729]
+- Add `key/value` mode for SQL module. {issue}15770[15770] {pull]15845[15845]
+- Add STAN dashboard {pull}15654[15654]
 - Add support for Unix socket in Memcached metricbeat module. {issue}13685[13685] {pull}15822[15822]
 
 *Packetbeat*

metricbeat/docs/modules/sql.asciidoc

@@ -30,7 +30,7 @@ metricbeat.modules:
 
   driver: "postgres"
   sql_query: "select now()"
-
+  sql_response_format: table
 ----
 
 [float]

x-pack/metricbeat/metricbeat.reference.yml

@@ -988,7 +988,7 @@ metricbeat.modules:
 
   driver: "postgres"
   sql_query: "select now()"
-
+  sql_response_format: table
 
 #--------------------------------- Stan Module ---------------------------------
 - module: stan

x-pack/metricbeat/module/sql/_meta/config.yml

@@ -6,4 +6,4 @@
 
   driver: "postgres"
   sql_query: "select now()"
-
+  sql_response_format: table