Update MongoDB protocol to use ECS fields

That dashboard was updated too.

Here's a summary of what fields changed.

Part of #7968

Changed

- bytes_in -> source.bytes
- bytes_out -> destination.bytes
- responsetime -> event.duration (unit are now nanoseconds)

Added

- destination
- event.dataset = mongodb
- event.end
- event.start
- network.bytes
- network.community_id
- network.protocol = mongodb
- network.transport = tcp
- network.type
- source

Removed

- mysql.iserror - It was a boolean that reflected the same information as `status` which uses OK or Error.

Unchanged Packetbeat Fields

- method
- resource
- query
- status
- type = mongodb (we might remove this since we have event.dataset)

CHANGELOG.next.asciidoc

@@ -68,6 +68,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Changed DHCPv4 protocol fields to align with ECS. {pull}10089[10089]
 - Changed AMQP protocol fields to align with ECS. {pull}10090[10090]
 - Changed HTTP protocol fields to align with ECS. {pull}9976[9976]
+- Changed MongoDB protocol fields to align with ECS. {pull}10158[10158]
 
 *Winlogbeat*