Add --force flag to modify annotations and labels

[2opremio]

This change adds a new flag (--force) to commands edit add annotation and edit add label so that annotations and labels are modified if they already existed.

Fixes #564

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[2opremio]

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[2opremio]

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[Liujingfang1]

@2opremio Thank you for working on this.

/lgtm
/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: 2opremio, Liujingfang1

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