[Metricbeat] Revisit MySQL module

[sorantis]

Today MySQL module collects many relevant metrics, however some are missing. E.g.

• innodb rows {deleted, updated, read, inserted}
• slow queries
• row locks
• CPU time spent by MySQL process
• cache stats (SHOW STATUS LIKE "qcache%"), including cache size.
• buffer pool size (innodb_buffer_pool_size)
• connection errors (SHOW GLOBAL STATUS LIKE 'Connection_errors%';)
• database keyword to use for filtering

[elasticmachine]

Pinging @elastic/integrations-services (Team:Services)

[tomsommer]

You can add SHOW PROCESSLIST and per-user information from performance-schema to this.

[sayden]

Today MySQL module collects many relevant metrics, however some are missing. E.g.

* innodb rows {deleted, updated, read, inserted}

* slow queries

* row locks

* CPU time spent by MySQL process

* cache stats (`SHOW STATUS LIKE "qcache%"`), including cache size.

* buffer pool size (innodb_buffer_pool_size)

* connection errors (`SHOW GLOBAL STATUS LIKE 'Connection_errors%';`)

* database keyword to use for filtering

Opened PR here #19844

You can add SHOW PROCESSLIST and per-user information from performance-schema to this.

Opened PR here #19851