Test for `tag_push` events webhook sends `push` payload
### Summary
The *Tag push events* test button in the *System Hooks* page doesn't send a `tag_push` event payload to the hook.
### Steps to reproduce
- Add a system hook and tick *Tag push events*
- Click on the *Test* button of the hook, then on *Tag push events*
### What is the current *bug* behavior?
The payload is of `push` type
### What is the expected *correct* behavior?
The payload should be of `tag_push` type
### Relevant logs and/or screenshots

This is the sent payload:
```
app_1 | {'after': 'da1560886d4f094c3e6c9ef40349f7d38b5d27d7',
app_1 | 'before': '95790bf891e76fee5e1747ab589903a6a1f80f22',
app_1 | 'checkout_sha': 'da1560886d4f094c3e6c9ef40349f7d38b5d27d7',
app_1 | 'commits': [{'author': {'email': 'test@example.com', 'name': 'Test User'},
app_1 | 'id': 'c5feabde2d8cd023215af4d2ceeb7a64839fc428',
app_1 | 'message': 'Add simple search to projects in public area',
app_1 | 'timestamp': '2013-05-13T18:18:08+00:00',
app_1 | 'url': 'https://test.example.com/gitlab/gitlabhq/commit/c5feabde2d8cd023215af4d2ceeb7a64839fc428'}],
app_1 | 'event_name': 'push',
app_1 | 'message': 'Hello World',
app_1 | 'object_kind': 'push',
app_1 | 'project_id': 15,
app_1 | 'ref': 'refs/heads/master',
app_1 | 'total_commits_count': 1,
app_1 | 'user_avatar': 'https://s.gravatar.com/avatar/d4c74594d841139328695756648b6bd6?s=8://s.gravatar.com/avatar/d4c74594d841139328695756648b6bd6?s=80',
app_1 | 'user_email': 'john@example.com',
app_1 | 'user_id': 4,
app_1 | 'user_name': 'John Smith'}
```
#### Results of GitLab environment info
<details>
<summary>Expand for output related to GitLab environment info</summary>
<pre>
System information
System:
Current User: root
Using RVM: no
Ruby Version: 2.4.4p296
Gem Version: 2.6.14.1
Bundler Version:1.16.5
Rake Version: 12.3.1
Redis Version: 3.0.6
Git Version: 2.19.0
Sidekiq Version:5.1.3
Go Version: unknown
GitLab information
Version: 11.3.0
Revision: 17bd59ad
Directory: /home/git/gitlab
DB Adapter: postgresql
URL: http://localhost:10080
HTTP Clone URL: http://localhost:10080/some-group/some-project.git
SSH Clone URL: ssh://git@localhost:10022/some-group/some-project.git
Using LDAP: no
Using Omniauth: yes
Omniauth Providers: oauth2_generic
GitLab Shell
Version: 8.3.3
Repository storage paths:
default: /home/git/data/repositories
Hooks: /home/git/gitlab-shell/hooks
Git: /usr/bin/git
</pre>
</details>
#### Results of GitLab application Check
<details>
<summary>Expand for output related to the GitLab application check</summary>
<pre>
Warning
You are running as user root, we hope you know what you are doing.
Things may work/fail for the wrong reasons.
For correct results you should run this as user git.
Checking GitLab Shell ...
GitLab Shell version >= 8.3.3 ? ... OK (8.3.3)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:root, or git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ...
1/1 ... ok
Running /home/git/gitlab-shell/bin/check
Check GitLab API access: OK
Redis available via internal API: OK
Access to /home/git/.ssh/authorized_keys: OK
gitlab-shell self-check successful
Checking GitLab Shell ... Finished
Checking Sidekiq ...
Running? ... no
Try fixing it:
sudo -u git -H RAILS_ENV=production bin/background_jobs start
For more information see:
doc/install/installation.md in section "Install Init Script"
see log/sidekiq.log for possible errors
Please fix the error above and rerun the checks.
Checking Sidekiq ... Finished
Reply by email is disabled in config/gitlab.yml
Checking LDAP ...
LDAP is disabled in config/gitlab.yml
Checking LDAP ... Finished
Checking GitLab ...
Git configured correctly? ... no
Trying to fix error automatically. ...Failed
Try fixing it:
sudo -u git -H "/usr/bin/git" config --global core.autocrlf "input"
For more information see:
doc/install/installation.md in section "GitLab"
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... skipped (no tmp uploads folder yet)
Init script exists? ... yes
Init script up-to-date? ... yes
Projects have namespace: ...
1/1 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.5 ? ... yes (2.4.4)
Git version >= 2.9.5 ? ... yes (2.19.0)
Git user has default SSH configuration? ... yes
Active users: ... 2
Checking GitLab ... Finished
</pre>
</details>
issue