Use dart-sass instead of node-sass

[BSFishy]

Is your feature request related to a problem? Please describe.

node-sass is a deprecated module that is not very well maintained.

Describe the solution you'd like

node-sass should be replaced with dart-sass. dart-sass (or just plain sass on npm) is a newer pure Javascript implementation of Sass that is much better maintained and will support us better in the future. Dashboards has already made this change.

[BSFishy]

This may need to be something we take care of when we revamp the theming system. Currently, we use sass-vars-to-js-loader, which has a dependency on node-sass. So we would either need to replace that (which it doesn't look like there is a good 1:1 replacement as of now) or wait until we don't need it anymore.

[ashwin-pc]

A similar migration was mad in OSD for reference. opensearch-project/OpenSearch-Dashboards#2054

[BSFishy]

Finished in #1001