feat(api): enhance Actions Secrets Management API for repository (#30656)

feat(api): enhance Actions Secrets Management API for repository (#30656)

- Add endpoint to list repository action secrets in API routes
- Implement `ListActionsSecrets` function to retrieve action secrets
from the database
- Update Swagger documentation to include the new
`/repos/{owner}/{repo}/actions/secrets` endpoint
- Add `actions` package import and define new routes for actions,
secrets, variables, and runners in `api.go`.
- Refactor action-related API functions into `Action` struct methods in
`org/action.go` and `repo/action.go`.
- Remove `actionAPI` struct and related functions, replacing them with
`NewAction()` calls.
- Rename `variables.go` to `action.go` in `org` directory.
- Delete `runners.go` and `secrets.go` in both `org` and `repo`
directories, consolidating their content into `action.go`.
- Update copyright year and add new imports in `org/action.go`.
- Implement `API` interface in `services/actions/interface.go` for
action-related methods.
- Remove individual action-related functions and replace them with
methods on the `Action` struct in `repo/action.go`.

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Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Signed-off-by: appleboy <appleboy.tw@gmail.com>