pkg/tz(ticdc): use correct ctx to get timezone (#8799)

[ti-chi-bot]

This is an automated cherry-pick of #8799

What problem does this PR solve?

Issue Number: ref #8798

What is changed and how it works?

• Fix a bug that unescape the timezone value twice
• Fix a bug we use the wrong ctx when we get the timezone.
• Warning when users use time-zone="" in sink-uri.
• Warning when users do not set the timezone in sink-uri

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)
  • pkg/tz(ticdc): use correct ctx to get timezone #8799 (comment)
  • pkg/tz(ticdc): use correct ctx to get timezone #8799 (comment)

Questions

Will it cause performance regression or break compatibility?

None

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

None

Release note

Fix the bug that TiCDC always uses `UTC` when creating changefeed

[ti-chi-bot]

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[hi-rustin]

/merge

[ti-chi-bot]

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

Commit hash: be52caf