[Metricbeat] Update MySQL dashboard (#19913) (#20024)

(cherry picked from commit c915bf7)

Author: sayden

CHANGELOG.next.asciidoc

@@ -668,6 +668,7 @@ field. You can revert this change by configuring tags for the module and omittin
 - The `elasticsearch-xpack/index` metricset now reports hidden indices as such. {issue}18639[18639] {pull}18706[18706]
 - Adds support for app insights metrics in the azure module. {issue}18570[18570] {pull}18940[18940]
 - Added cache and connection_errors metrics to status metricset of MySQL module {issue}16955[16955] {pull}19844[19844]
+- Update MySQL dashboard with connection errors and cache metrics {pull}19913[19913] {issue}16955[16955]
 
 *Packetbeat*