gogs-webhook didn't support gogs release event

- Gogs version (or commit ref):
- Jenkins version: Jenkins ver. 2.107.3
- Jenkins modules used in combination with gogs-webhook-plugin:
- JSON Output of webhook: {"result":"ERROR","message":"Only push event can be accepted."}

## Description
I had tried to config my gogs system to support auto release my test version to work version.
so i hope in gogs system create one repo version , it will send out one webhook event . in fact, gogs had
support the funciton. i had choosed event of repo release . it give out this post data:

Request URL: http://jenkins.address/gogs-webhook/?job=releasedb/copytest
Request method: POST
Content-Type: application/json
X-Gogs-Delivery: 7f96dbfc-c93a-4247-8528-0c7e1566c53d
X-Gogs-Event: release
X-Gogs-Signature: 03cfb231c9c643277fae62bd318538e9e77157c630cb1373e7f37ab84cc14e94

I had read gogs=webhook source code , in webhook.java , it only receive "push" event.
so , i hope it can add "release" and other's event.

thx.

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