Optimize gc safepoint advancing for internal transaction

[TonsnakeLin]

Enhancement

TiDB advances gc safepoint every tidb_gc_run_interval time with step tidb_gc_life_time. If there is a long time transaction from user client lives more than tidb_gc_life_time, the safpoint can't be advanced until the long transaction is finished or lives than 24h. This mechanism ensures the continuous advancement of gc safepoint and ensures that the data that active transactions need to access will not be cleared.
However, Internal transactions run in TiDB don't comply with the mechanism above. If the internal transaction lives more than tidb_gc_life_time, maybe failed because the data it needs to access was cleared.
Here is an example that an auto analyze task run failed when it lived more than 20 minutes because the data was cleared. The TiDB log printed [tikv:9006]GC life time is shorter than transaction duration, transaction starts at 2021-11-17 14:09:54.756 +0800 CST, GC safe point is 2021-11-17 14:11:54.755 +0800 CST

[jackysp]

The most of internal transactions should not exceed 10min. Also, I seem to see that the planner group is trying to expose auto analyze to the public, for example in the processlist at #31724. Does this mean that there is no need to change
the current mechanism? One more question, for analyze it uses max int64 to read the data itself, and it doesn't require high accuracy of data, so is it not worth to let it block GC?

[TonsnakeLin]

PR #32726 unified all internal transactions startTS and GC advances SafePoint considering them
and I'm sure you add auto analyze to processlist is totally useless to gc advancing safpoint, The ProcessInfo.CurrTxnStartTS always 0.
[2022/04/02 18:03:59.377 +08:00] [INFO] [session.go:3207] [linpinfaxian] [sessionTS=0]
[2022/04/02 18:03:59.468 +08:00] [INFO] [session.go:3207] [linpinfaxian] [sessionTS=0]
@jackysp