V4 API: Remove deprecated MR and Issue endpoints and preserve V3 namespace

Closes #27180

See merge request !8967

Make all system notes lowercase

See merge request !8807

Modify the search bar area on admin/projects page

Closes #26794

See merge request !8776

Resolves user avatar flickers as you type

Closes #27602

See merge request !8950

Use babel to transpile all non-vendor javascript assets regardless of file extension

See merge request !8988

fix ace editor modules to include asset digest in production

See merge request !8869

Introduce maximum session time for terminal websocket connection

Closes #26263

See merge request !8413

Unify projects search by removing /projects/:search endpoint

Closes #22007

See merge request !8877

API: Fix file downloading

See merge request !8953

Store the value in application settings.
Expose the value to Workhorse.

Add index to labels for `type` and project_id`

Closes #27676

See merge request !8978

Fixed typo in slash commands docs

Closes #27674

See merge request !8976

When loading pages that display the number of open issues,
the backend runs a query such as:

```sql
SELECT "labels"."id" FROM "labels" WHERE "labels"."type" IN ('ProjectLabel') AND "labels"."project_id" = 1000
```

This results in an entire scan of the `labels` table. To optimize performance,
add the appropriate index to the table.

Closes #27676

Fix "NameError: uninitialized constant Rack::Proxy" in production environment

See merge request !8977

Fixes gitlab-org/gitlab-ce#27674

UX Guide: Button placement in groups

See merge request !8972

Integrate webpack for frontend asset compilation

Closes #14634

See merge request !7288

Document that the retro and kickoff notes are public

See merge request !8788

* master:
  Change window size before visiting page, to get correct scroll position
  Fix slash commands spec error
  Move project services to new location under Integrations
  Move webhooks to new a location under Integrations
  Fixed eslint test failure
  Fixed redirection from http://someproject.git to http://someproject
  Add traits for the different Event types to the Event factory
  prevent nonewline type diff lines from containing unfolding link
  ensure linenumber data attribute is correct for the last line in a diff chunk
  ensure last line in diff block is contained within a table row element
  ensure click event is bound only once

Resolve "Line numbers are off in dynamically loaded diff chunks"

Closes #26300

See merge request !8428

Change window size before visiting page, to get correct scroll position

See merge request !8963

Fix slash commands spec error

See merge request !8968

Redirect http://someproject.git to http://someproject

Closes #26275

See merge request !8951

Refactor integrations page documentation

See merge request !8966