System-wide webhooks (#10546)

* Create system webhook column (and migration)

* Create system webhook DB methods

Based on the default webhook ones

* Modify router to handle system webhooks and default ones

* Remove old unused admin nav template

* Adjust orgRepoCtx to differentiate system and default webhook URLs

* Assign IsSystemWebhook when creating webhooks

* Correctly use booleans for IsSystemWebhook

* Use system webhooks when preparing webhooks for payload

* Add UI and locale changes

* Use router params to differentiate admin hook pages

* Fix deleting admin webhooks and rename method

* Add clarity to webhook docs

* Revert "Remove old unused admin nav template"

This reverts commit 191a20a738.

* Rename WebHooksNewPost to GiteaHooksNewPost for clarity

* Reintroduce blank line lost during merge conflict

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: Lauris BH <lauris@nix.lv>

templates/admin/navbar.tmpl

@@ -14,6 +14,9 @@
 	<a class="{{if .PageIsAdminHooks}}active{{end}} item" href="{{AppSubUrl}}/admin/hooks">
 		{{.i18n.Tr "admin.hooks"}}
 	</a>
+	<a class="{{if .PageIsAdminSystemHooks}}active{{end}} item" href="{{AppSubUrl}}/admin/system-hooks">
+		{{.i18n.Tr "admin.systemhooks"}}
+	</a>
 	<a class="{{if .PageIsAdminAuthentications}}active{{end}} item" href="{{AppSubUrl}}/admin/auths">
 		{{.i18n.Tr "admin.authentication"}}
 	</a>