docs: add RFC for service webhook auto-repair mechanism

[krisxia0506]

What this PR does / Why we need it:

This PR proposes an auto-repair mechanism for service webhooks that have been manually deleted from code repositories (GitLab/GitHub/Gerrit/Gitee).

Current Problem:

• When webhooks are manually deleted from repositories (e.g., cleanup, migration, accidental deletion), the system cannot automatically recover them
• Code changes can no longer trigger workflows after webhook deletion
• Users must manually delete and recreate services to restore webhook functionality

Solution:
During service updates, the system will automatically:

1. Verify webhook existence using the stored HookID from the webhook collection
2. Detect if the webhook has been deleted from the repository
3. Automatically recreate the webhook if missing

This eliminates manual intervention and ensures continuous webhook availability.

What is changed and how it works?

Design Document: community/rfc/2025-01-10-service-webhook-auto-repair.md

Key Changes:

1. Add webhook verification interface for all Git platform clients:
   - GitLabClient.WebHookExists(owner, repo, hookID)
   - GitHubClient.WebHookExists(owner, repo, hookID)
   - GerritClient.WebHookExists(repo, remoteName, hookID)
   - GiteeClient.WebHookExists(owner, repo, hookID) (public/private)
2. Modify ProcessServiceWebhook to add verification logic:
   - Only verify during service updates (not during creation)
   - Execute asynchronously using goroutine to avoid blocking
   - Verification failures do not affect the main workflow
3. Implement verification and repair functions:
   - VerifyAndRepairWebhook(): Query webhook record, verify existence, recreate if missing
   - checkWebhookExists(): Platform-specific webhook verification

Workflow:

  Service Update
    ↓
  ProcessServiceWebhook
    ├─ ProcessWebhook (existing: compare DB records, add/remove webhooks)
    └─ [NEW] Verify and repair webhook (async)
         ├─ Query webhook record from DB (get HookID)
         ├─ Call Git platform API to verify webhook existence
         └─ If not found: delete old record → recreate webhook

Multi-platform Support:

• GitHub (github)
• GitLab (gitlab)
• Gerrit (gerrit)
• Gitee Public Cloud (gitee)
• Gitee Private Deployment (gitee-enterprise)

Key Constraints:

• Non-invasive: failures do not block service updates
• Async execution: uses goroutine, no performance impact
• Backward compatible: leverages existing webhook collection and HookID field

Does this PR introduce a user-facing change?

User-Facing Impact:

• Improved availability: Webhooks are automatically repaired without manual intervention

• No breaking changes: Completely backward compatible, no API or database modifications required

• Transparent to users: Auto-repair happens in the background during service updates

• Fixes existing issue: Resolves the problem where manually deleted webhooks cannot be recovered

• API change

• database schema change

• upgrade assistant change

• change in non-functional attributes such as efficiency or availability

• fix of a previous issue