Fixes #24124: Links and buttons don't have the right colour since the bootstrap update

[RaphaelGauthier]

https://issues.rudder.io/issues/24124

There's still a lot of optimisation to be done on this (like replacing all our colour codes with variables, making sure we override as few bootstrap rules as possible but instead using variable overrides, etc.) but to limit its scope I've just fixed and harmonised the appearance of Rudder's main links and buttons.

This first PR already brings a few changes:

• There is a new _rudder-variables.scss file

  • the underscore means in Sass that this is a "partial" file, i.e. a file that will only be imported into other scss files. It is not compiled in css
  • it will contain all our colour codes (text, buttons, compliance, policy mode, warning/error etc.). Only variables, no css rules!
  • It is completely independent of bootstrap
  • In future, the code in this file will be divided into several partial files, and all these files will be imported into this file, which will serve as the root, to make code maintenance easier.

• We no longer load the bootstrap.css file directly into common-layout.html, instead I've created a new rudder-bootstrap.scss file into which bootstrap is imported. This allows :

  • cleanly override bootstrap variables
  • have a file where you can find all the overridden bootstrap rules
  • in the future, not to import ALL bootstrap, but only the modules that interest us

[RaphaelGauthier]

Commit modified

[RaphaelGauthier]

Commit modified

[RaphaelGauthier]

Commit modified

[Normation-Quality-Assistant]

OK, merging this PR