sorter(ticdc): use correct cgroup memory limit in some scenarios (#8589)

[ti-chi-bot]

This is an automated cherry-pick of #8589

What problem does this PR solve?

Issue Number: close #8588

What is changed and how it works?

Use a better way to fetch cgroup memory limit.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Have been verified in the following scenarios

• systemd cgroup enabled
• systemd cgroup not enabled
• docker run container under containerd-shim-runc-v2 with memory limit
• docker run container under containerd-shim-runc-v2 without memory limit
• K8s starts pod with memory limit
• K8s starts pod without memory limit

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Use correct cgroup memory limit in sorter engine under some scenarios.

[ti-chi-bot]

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[amyangfei]

/merge

[ti-chi-bot]

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

Commit hash: bf9c4f9

[amyangfei]

/run-dm-integration-test