Print Txn ID and Query ID in log to trace the whole lifetime of a Txn / SQL

[breezewish]

Feature Request

Is your feature request related to a problem? Please describe:

TiDB now outputs TxnStartTs or ConnId in logs, which is not sufficient.

Cons of TxnStartTs:

• A transaction may include multiple SQLs. Cannot distinguish different SQLs in the same transaction.
• TxnStartTs may not be unique even for different transactions, e.g. it can be MaxUint64.

Cons of ConnId:

• A connection can send multiple SQLs or transactions, cannot distinguish.
• ConnId is even not send to TiKV so that TiKV and TiDB logs cannot be linked together.

Describe the feature you'd like:

• For each transaction, assign a globally unique TxnId. The id can be generated by randomize in uint64.

• For each query, assign a globally unique QueryId. The id can be generated by randomize in uint64.

• Both TiDB and TiKV logs outputs the TxnId and QueryId, for example, in slow logs, conflict logs, back off logs, etc.

This simplifies the process to diagnose problems from logs: users should be able know everything (log) about a transaction by only grep the TxnId, and know everything (log) about a query by only grep the QueryId.

Describe alternatives you've considered:

TxnId and QueryId can be derived from a global Connection Id, in order to be able to associate Transaction / Query with Connection. However looks like it doesn't need to be this complicated, since we can print connection id in the log at the same time in the log together with TxnId and QueryId. In this way, user can know the connection id by simply grep either TxnId or QueryId.

Teachability, Documentation, Adoption, Migration Strategy:

[breezewish]

Related task: #15638