[APM] Add telemetry for transaction types

[dgieselaar]

We are considering showing stats for the default transaction types (page-load, request) only in 7.11. We should add telemetry for the 7.10 release that will tell us:

• how many services do not have data for the default transaction types
• the cardinality of transaction.type

Sampling data from the last 24 hours should be enough.

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[botelastic]

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