Modify keycloak vanilla theme to be parametrized

[laskasn]

Keycloak vanilla theme should be kept "generic" meaning that it should not be aware of anything regarding its installations.
The theme should be kept in a repository, and any specific installation parameters should be kept in different repository/ies, which parametrize the vanilla theme.
The vanilla theme should be able to be parametrized by configuration files (containing icons, text captions, etc).

[laskasn]

Created the first version, it's the master branch here.
Each other branch, does not have any code, but instead a configuration file, along with a github action to release the parametrized theme (jar). For instance see the dissco branch.
The relase 1.0 for dissco can be found here

We need to add more config parameters (i.e. for footer, for additional icons, etc), so i leave this ticket open