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

This allows users to configure the number of points stored in a single
UDP packet. This in turn can be used to reduce the number of UDP packets
being sent at the cost of these packets being somewhat larger.

The default setting is 1 point per packet so nothing changes for
existing users.