Add metrics the number of running transactions

[SongJXin]

Add the mysql_info_schema_innodb_trx_running_transactions metric to count the number of currently active InnoDB transactions. You can use the collector.info_schema_innodb_trx.running_time parameter to count transactions that started a certain number of minutes ago.

# HELP mysql_info_schema_innodb_trx_running_transactions Number of running transactions that have been running for more than the specified time.
# TYPE mysql_info_schema_innodb_trx_running_transactions gauge
mysql_info_schema_innodb_trx_running_transactions 0