Add Corteza studio UI personalization feature

[KinyaElGrande]

Ref: #1267

Corteza Studio PR

This PR introduces a new feature that empowers users to personalize Corteza web applications according to their preferences using corteza main sass variables as branding parameters [white, black, primary, secondary, success, warning, danger, light,extra-light, dark, tertiary, gray-200, body-bg]. Something to note, however, when a sass variable for example $primary is defined in the custom CSS editor, it will take precedence over branding variables.
In case of any sass-related error, the default CSS which is compiled and minified Bootstrap SASS, Bootstrap-Vue SASS and custom-webapp sass variables will be returned.

Additionally, SASS support has been integrated into the Corteza Server. However, users will need to install Dart-SASS locally or in the deployment environment, as detailed in the setup instructions provided here.

Major change introduced

Most of the SASS processing has been moved to the BE this includes; Bootstrap SASS, Bootstrap-Vue SASS, and custom webapp sass variables.

It is important to note that this change hasn't affected Custom CSS functionality

Branding Editor Screenshot

Video demo

corteza-studio.mov

Checklist when submitting a final (!draft) PR

• Commits are tidied up, squashed if needed and follow guidelines in CONTRIBUTING.md
• Code builds
• All existing tests pass
• All new critical code is covered by tests
• PR is linked to the relevant issue(s)
• Rebased with the target branch

[tjerman]

We'll need to do a bit of refactoring to clean it up and make it a bit friendlier to use. Also, please rebase so my changes don't show up in the diff (needles bloating).

Other then that, back-end stuff looking decent already

[tjerman]

Some meta bits here and there

[tjerman]

1+1 bits left; do take a quick look please

[tjerman]

I think this looks decent now!

What I'd consider is making the system service not just clear out the cache, but do the actual re-computation. It'll probably not change much, but could be a bit better.

[tjerman]

A few notes but lgtm as before 👍

[katrinDY]

• Getting this issue in compose:

- Getting this is err when I open Custom CSS editor modal  - Think it's a good idea to add a way to undo a color change. Maybe add a set to default btn. If I change a color and wanna undo it, I gotta change the page and go back to UI settings. :( Discuss with Jože before hopping onto this - Color changes in admin aren't applied to privacy, reporter, and wf - Colors in privacy, reporter, and wf aren't the default ones - Please, rebase with .9 because the submit btn for custom css is missing. Can't submit changes without the btn

[KinyaElGrande]

@katrinDY good observation I almost missed that..I've fixed that on my latest commit.