metric: distinguish the internal and general transactions in metric

[cfzjywxk]

Enhancement

By now all the metrics in the tidb-transction would be displayed for both the background internal transactions and user transactions, it's sometimes misleading to diagnose user transaction issues. It's better to separate them and display the user transaction information by default.

• Refactor the transaction metrics and panel in tidb.json, and distinguish them with General and Internal flags, the tidb part.
• Refactor the transaction metrics and panel in tidb.json, and distinguish them with General and Internal flags, the client-go part.