add slack notifications for wiki pages

## What does this MR do?

Lets the Slack service be configured to send notifications when wiki pages are created or edited.

## Are there points in the code the reviewer needs to double check?

I'm just starting to get familiar with the Gitlab codebase and I was unsure on how to get the wiki page url to pass it to the slack message, on whether or not I needed to refactor the create/update methods for wiki pages from the controller to a service (but seemed necessary to test it better), and if I needed to add a column to the web hooks table or if the services table would have been enough. Please let me know if I should change anything and I will improve the MR, thanks for checking :)

## Why was this MR needed?

Related to #563 and fixes #4233.



See merge request !2998

Add raw build trace output

Closes #15308, #15147

Changes in the UI:

- on finished build:

    ![raw-on-finished-build](/uploads/0e0904940db5b381ae064d49343c6508/raw-on-finished-build.png)

- on running build:

    ![raw-on-running-build](/uploads/0e4c800b68c12bdd0cbd2eea732b22ff/raw-on-running-build.png)

See merge request !3767

License templates when creating/editing a LICENSE file

Closes #12804

See merge request !3660

update changelog

Fix javascript errors with invalid json because of commas

fixes #15390 

See merge request !3827

[ci skip]

Define constants only if not defined yet and freeze them

Fixes #15139.

See merge request !3810

Remove XSS vulnerability in Label and Milestone dropdowns

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15389

See merge request !1951

Fix GitHub project's link in the import page when provider has a custom URL

Closes gitlab-org/gitlab-ee#478

See merge request !3803

use ! rather than # for merge request references

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/15278

See merge request !3740

Sanitize branch names for confidential issues

- When creating new branches for confidential issues, prefer a branch name like `issue-15` to `some-sensitive-issue-title-15`.
- The behaviour for non-confidential issues stays the same.

Closes #14566

See merge request !3671

Configuring of points per UDP packet

Related to https://gitlab.com/gitlab-com/operations/issues/195. This option would allow us to experiment with finding a good balance between points-per-packet and the UDP packet size.

cc @pcarranza 

See merge request !3816

Bump version to 8.8.0-pre

See merge request !3809

"git lfs init" is deprecated, use "git lfs install" instead.

Recent releases of git-lfs warn that "init" is a deprecated command and that "install" should be used.


See merge request !3779

Remove persistent XSS vulnerability in `commit_person_link` helper

Because we were incorrectly supplying the tooltip title as
`data-original-title` (which Bootstrap's Tooltip JS automatically
applies based on the `title` attribute; we should never be setting it
directly), the value was being passed through as-is.

Instead, we should be supplying the normal `title` attribute and letting
Rails escape the value, which also negates the need for us to call
`sanitize` on it.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15126

See merge request !1948

Removed aside toggle on profile pages

Closes #13943

See merge request !3796

Trigger filtering after ajax is complete in dropdown

![filter](/uploads/1c361d968769eb3fe5cdd05dee497aa6/filter.gif)

Closes #15186

See merge request !3813