BD-39 modernize paragon for edx-platform

[leangseu-edx]

https://openedx.atlassian.net/wiki/spaces/COMM/pages/2531557626/BD-39+Technical+Discovery+Upgrade+Frontend+Frameworks+in+edx-platform

Success✅

• Upgrade paragon to version 20
• upgrade sass compiler and successfully compile
• upgrade bootstrap to 4.6.2
• Theming
  • https://github.com/edx/edx-themes/blob/master/docs/guides/local-development.rst

Step by step for deploying

• deploy within sandbox
• deploy to stage
• deploy to prod

Honorable mention

This is a manual merging because of the error I received from package-lock.json. There a combine of multiple pr that was part of this:
(1) Prepare edx.org-next theme for Libsass upgrade
https://github.com/edx/edx-themes/pull/737
(2) Upgrade Libsass in platform
https://github.com/edx/edx-platform/pull/27683
(3) Upgrade Bootstrap to 4.6.0
https://github.com/edx/edx-platform/pull/27751
(4) Swap Bootstrap for Paragon and fix visual regressions
https://github.com/edx/edx-platform/pull/27771

[kdmccormick]

This work has stalled. See #31616.

[kdmccormick]

I see that many many !optional flags have been added. I believe this is because we were relying on bugged behavior in (upstream) libsass 3.3.2, which is what is used in libsass 0.10.0.