Signed-off-by: NTakuya Noguchi <takninnovationresearch@gmail.com>

Some dependencies have incompatibilities with Node v12, which will
become LTS in October. Namely node-sass and needed to be forwarded in
order for their native extensions to compile without errors.

- Created scripts/frontend/test.js
- Updated test task to call Node script

pdf.js is available on npm. Importing the dependency from there instead
of vendoring it has certain benefits, e.g. the discoverability of
updates (especially security fixes).

We were using 8.0.0-rc.8 previously, and there appears to be significant
new dependencies.

Implemented the toast component for success messages

Does not run stylelint for the vendors folder

Resolves an issue where long series label names overflow
the popover chart tooltip container

Adding support for metrics alerts disabled multiple query support.
To avoid a data model refactor, this enables the visual of multiple
queries per chart on the front end, combining queries based on
metric group, title, and y-axis label.

This also adds support for adding and editing alerts based on the
query selected rather than the single metric associated with the chart.

Remove unneeded var for webpack-prod call in gitlab-ci

This resolved the one conflict we have in CE/EE.

# Conflicts:
#   package.json

Upgrade to latest Version

DRYed the code

Changed new rules to warnings

Manual prettified and added stylelint rules

This reverts merge request !26380