mounter(ticdc): enum type default value set explicitly to avoid wrong enum value fetched by the encoder (#9262)

[ti-chi-bot]

This is an automated cherry-pick of #9262

What problem does this PR solve?

Issue Number: close #9259

What is changed and how it works?

• mounter set the default value for the enum type explicitly, to make enum.Value set correctly.

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

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

Release note

`None`

[3AceShowHand]

/merge

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[3AceShowHand]

/merge

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CharlesCheung96, sdojjy

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[3AceShowHand]

/merge

[ti-chi-bot]

@3AceShowHand: We have migrated to builtin LGTM and approve plugins for reviewing.

Please use /approve when you want approve this pull request.

The changes announcement: LGTM plugin changes

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.