session,sessionctx: enable tidb_enable_paging by default

[tiancaiamao]

What problem does this PR solve?

Issue Number: close #35273

Problem Summary:

Please review #35244 first, this is based on that PR.

What is changed and how it works?

Set the default tidb_enable_paging value to true.
For the newly bootstraped cluster, the global variable tidb_enable_paging is set.
For the old cluster, the default value is not changed.

The would make us cover the bugs as soon as possible before the next release.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

For a newly bootstraped cluster, the default value of `tidb_enable_paging` is true. The coprocessor paging protocol is enabled by default. For existing cluster, the default value is still false unless the user set it explicitly. 

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• XuHuaiyu
• wshwsh12

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[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/2e4ebf4d5586ece5245b6942669db5ea8e78781a

[tiancaiamao]

/run-check_dev_2

[tiancaiamao]

ref #35633

[ti-chi-bot]

@tiancaiamao: PR needs rebase.

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[tiancaiamao]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 2e4ebf4

[tiancaiamao]

/run-realtikv-test

[tiancaiamao]

/run-mysql-test

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! New failing [2] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/integration-common-test	🟥 failed 1, success 10, total 11	34 min	New failing
idc-jenkins-ci-tidb/tics-test	🟥 failed 1, success 0, total 1	3 min 55 sec	New failing
idc-jenkins-ci/integration-cdc-test	🟢 all 35 tests passed	23 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 12 tests passed	12 min	Existing passed
idc-jenkins-ci-tidb/integration-ddl-test	🟢 all 6 tests passed	7 min 14 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	6 min 55 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	5 min 45 sec	Existing passed
idc-jenkins-ci-tidb/mybatis-test	🟢 all 1 tests passed	2 min 54 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	2 min 40 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed