stale read query's slow-log doesn't record the StmtReadTS

[crazycs520]

Enhancement

Stale-read query without in txn, it'sTxn_start_ts in slow-log is 0, it is not friendly to debug. We may need to record StmtReadTS in Txn_start_ts or use another field to distinct with Txn_start_ts.

Txn_start_ts is importance when investigating slow query.

# Time: 2023-07-25T05:01:38.109851486Z
# Txn_start_ts: 0
# User@Host: root[root] @ 10.0.1.1 [10.0.1.1]
# Conn_ID: 6134008245594882069
# Query_time: 0.011962068
# Parse_time: 0.000072619
# Compile_time: 0.000295058
# Rewrite_time: 0.00006279
# Optimize_time: 0.000132229
# Wait_TS: 0
# Cop_time: 0.007272851 Process_time: 0.000133309 Wait_time: 0.00002725 Request_count: 1 Process_keys: 11 Total_keys: 107 Get_snapshot_time: 0.000 Rocksdb_key_skipped_count: 116 Rocksdb_block_cache_hit_count: 4
# DB: test
# Is_internal: false
# Digest: e606e68eee8d6babf9e89d7a1920256260bad5a433b57b935b889e7d712ab22a
# Stats: t1:443091851964841991[215606;10347]
# Num_cop_tasks: 1
# Cop_proc_avg: 0.000133309 Cop_proc_addr: 10.0.1.9:20161
# Cop_wait_avg: 2.725e-05 Cop_wait_addr: 10.0.1.9:20161
# Mem_max: 22196
# Prepared: false
# Plan_from_cache: false
# Plan_from_binding: false
# Has_more_results: false
# KV_total: 0.007232282
# PD_total: 0
# Backoff_total: 0
# Write_sql_response_total: 0.004133461
# Result_rows: 2
# Succ: true
# IsExplicitTxn: false
# IsSyncStatsFailed: false
# Plan: tidb_decode_plan('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')
# Plan_digest: 68d93a0450a10996e3e7130586ce3087944adefb9360740ba24330ef95e26ed4
# Binary_plan: tidb_decode_binary_plan('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')
select pk, sk, ts, v, n from (             select pk, sk, ts, v, row_number() over (partition by pk, sk order by ts desc) as n             from t1 as of timestamp now() - interval 5 second where pk = '000000000000000000000000049956' and sk >= '0000' and sk < '0000-0001'         ) as tt where n <= 2 order by sk asc;