Let API create and edit system webhooks, attempt 2

[mbollmann-v]

This PR fixes inconsistencies between system and default webhooks in the Gitea API. (See also #26418)

• A system webhook is a webhook that captures events for all repositories.
• A default webhook is copied to a new repository when it is created.

Before this PR POST /api/v1/admin/hooks/ creates default webhooks (if not configured otherwise) and GET /api/v1/admin/hooks/ returns system webhooks.

The PR introduces an optional query parameter to GET /api/v1/admin/hooks/ to enable selecting if either default, system or both kind of webhooks should be retrieved. By default the flag is set to return system webhooks keep current behaviour.

Examples

System Webhooks

Create

POST /api/v1/admin/hooks/

{
  "type": "gitea",
  "active": false,
  "branch_filter": "*",
  "events": [ "create", "..." ],
  "config": {
    "url": "http://...",
    "content_type": "json",
    "secret": "secret",
    "is_system_webhook": true // <-- controls hook type
  }
}

List

GET/api/v1/admin/hooks?type=system //type argument is optional here since it's the default

Others

The other relevant endpoints work as expected by referencing the hook by id

GET /api/v1/admin/hooks/:id
PATCH /api/v1/admin/hooks/:id
DELETE /api/v1/admin/hooks/:id

Default Webhooks

Create

POST /api/v1/admin/hooks/

{
  "type": "gitea",
  "active": false,
  "branch_filter": "*",
  "events": [ "create", "..." ],
  "config": {
    "url": "http://...",
    "content_type": "json",
    "secret": "secret",
    "is_system_webhook": false // optional, as false is the default value
  }
}

List

GET/api/v1/admin/hooks?type=default

Others

The other relevant endpoints work as expected by referencing the hook by id

GET /api/v1/admin/hooks/:id
PATCH /api/v1/admin/hooks/:id
DELETE /api/v1/admin/hooks/:id

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