[SIEM integration] Standardize SQL information

[simitt]

As layed out in the design doc information related to SQL queries could be interesting to integrate with the SIEM app. Required steps are:

• [ ] participate in defining SQL field set in ECS https://github.com/elastic/ecs/issues/514
• [ ] create mock ups for SIEM integration
• [ ] investigate if additional information should be collected by APM agents
• [ ] Failures in SQL queries result in a dedicated error event. Investigate if the error information should be duplicated in the span capturing the SQL information or if the separation into two events linking from the error to the span is fine.

[simitt]

Following database/sql specific information is currently collected:

Field	indexed	used by APM UI
span.type	x
span.subtype	x
span.name	x
span.action	x
span.db.link	x
span.db.instance
span.db.statement		x
span.db.type		x
span.db.user

Moving fields that are indexed or used by the Kibana UI to another field is considered to be a breaking change. Since this is the majority of the db related fields, moving the information to future ECS aligned fields would be a breaking change.