Utilize the loading skeleton when trainers are being fetched

The tabs select the scope of environments to show, and are synced to the
URL query parameters.

Testing the tab selection is a little tricky due to the reactive poll
interval, so if there is no interval, just skip polling.

This is also good in the event polling is disabled.

This reverts merge request !75139

Fix URL

New filtered search

Fixes the collapsed assignees and reviewers
clickable areas caused by some extra margin and padding.

Whenever the user interacts with a merge request, the attention
request state for that user will be removed.
If the merge request is closed or merged, the attention
request is removed from all reviewers and assignees.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/345365

Disables the lock button when the current file is locked by another user

To collect the metrics on ci variables creation
we are adding tracking events
for the validation errors in the ci_variable modal

Changelog: added

- Added tests for author, assignee, reaction emoji, type, labels, epic, iteration and weight

Changelog: fixed

The new environments page was lacking the new environment and add review
apps buttons.

It has been tweaked slightly to take advantage of the action primary and
secondary props of the GlTabs, which means I can't take advantage of the
GlModalDirective anymore. Instead, I modify the modal to work via
v-model to show/hide the modal. This means that the adjustment for the
mobile view happens in the GlTabs component now, thereby making the app
component template smaller.

Addressed code review comments

Display a large button when PDF is too large to display

- source
- test

Changelog: added

The constants are moved to more appropriate directories

This removes the `configureIacScanningViaMr` feature flag that was
enabled by default in 14.6.

Changelog: removed

This change removes createAction from the `~/flash` interface and its
tests.

This helps reduce the surface area of features that create flash
has to support, so it can be refactored later.