WL#9628: Enable PFS transaction instrumentation by Default

In MySQL 5.7 we originally proposed to turn transaction instrumentation on in the 
default configuration of PFS (WL#8321)

This change was reverted due to a snafu in the proposal:
- The consumer was enabled
- The instrument was not

This WL is to propose that we enable both in MySQL 8.0:

 performance-schema-consumer-events-transactions-current=ON
 performance-schema-consumer-events-transactions-history=ON
 performance-schema-instrument='transaction%=ON'

User Documentation
==================

* https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-2.html
* https://dev.mysql.com/doc/refman/8.0/en/performance-schema-transaction-tables.html