feat(theme-generator): Add possibility to force custom color @angular/material:theme-color

### Feature Description

My problem is that I still can't understand how `@angular/material:theme-color` works. In the terminal, I need to provide colors for primary, secondary, and tertiary. For each one, I specify a single color, like #ff9500, because that's what I want.

`What HEX color should be used to generate the M3 theme? It will represent your primary color palette. (ex. #ffffff) **#005dba**
What HEX color should be used represent the secondary color palette? (Leave blank to use generated colors from Material) **#005dba**
What HEX color should be used represent the tertiary color palette? (Leave blank to use generated colors from Material) **#005dba**`

However, when generating the theme, I see that it creates color palettes, but when I try to get just my color, I use **`--mat-sys-primary`.** Unfortunately, it appears significantly darker (#8c5000), and I don't know which variable the color is actually hidden under. I have the impression that due to the low contrast, it is being artificially darkened. However, I selected the option not to generate mixins with high contrast. I would like to be able to use exactly that color without worrying about contrast. Currently, I am forced to manually change all the system token colors because the generated palette still interferes too much with what I want to achieve, taking away the flexibility I need in this case.

### Use Case

It would be great to be able to specify in the terminal that I want exactly the colors I mention, without any interference.

Commencez par le générateur @angular/material:theme-color et ses invites dans le terminal, puis comparez les couleurs demandées à la valeur --mat-sys-primary générée. Le travail est terminé lorsque les utilisateurs peuvent choisir d’utiliser exactement les couleurs spécifiées, sans que la palette générée ni les ajustements de contraste ne les remplacent.

Rédigé par le modèle d'indexation à partir du texte de l'issue.