Add the "contribution" label for GitHub issues created by external contributors

[qiancai]

Feature Request

• I have searched the issues of this repository and believe that this is not a duplicate.

Is your feature request related to an Issue or PR(Optional)

• Which project: pingcap/docs-cn, pingcap/docs, and pingcap/website-docs

Describe the feature you'd like:

Currently, ti-chi-bot only adds the "contribution" label for GitHub PRs created by external contributors, while creating issues and reporting bugs contribute to our documentation quality too. Adding the "contribution" label can serve as a form of recognition and encouragement for external contributors, highlighting their contributions and acknowledging their efforts.

Do you have any ideas on how to implement it?(Optional)

[ti-chi-bot]

Issues go stale after 90d of inactivity.
Mark the issue as fresh with /remove-lifecycle stale.
Stale issues rot after an additional 30d of inactivity and eventually close.
If this issue is safe to close now please do so with /close.
Send feedback to sig-community-infra or wuhuizuo.
/lifecycle stale

[ti-chi-bot]

Stale issues rot after 30d of inactivity.
Mark the issue as fresh with /remove-lifecycle rotten.
Rotten issues close after an additional 30d of inactivity.
If this issue is safe to close now please do so with /close.
Send feedback to sig-community-infra or Mini256.
/lifecycle rotten