[FEATURE] -improve template context

[oknozor]

Is your feature request related to a problem? Please describe.
While the current template system works it feels a bit messy.

The template context is updated using a Hashmap<String, String> , merging values from sub profiles in the global context.

Current templating system

We have a global variable file enabled in bombadil.toml

# File: dotfiles/bombadil.toml
[settings]
vars = [ "vars/vars.toml"  ]

Containing the following variables:

# File: dotfiles/vars/vars.toml
wallpaper = "$HOME/dotfiles/wallpapers/sea.jpg"
terminal = "alacritty"

We can overwrite wallpaper using an additional profile

# File: dotfiles/vars/themes/home.toml
wallpaper = "~/dotfiles/assets/wallpapers/night_sky_34i.jpg"

This works fine as long as we don't shallow a variable twice.
Currently it's hard to predict the final value of a variable when shallowing it multiple time in different profiles.

Describe the solution you'd like
tera allow to pass serde_json::Value in its context.
This would allow to write variable using all the toml semantic in a more structured way.

Example

# dotfiles/vars.toml
[colors]
blue = "#blue"
red = "#red"

[secrets]
passphrase = "some gpg encrypted value" 

[desktop.sway]
bar = "ironbar"
login_manager = "gtk-greet"

# or toml objects
desktop = [
  { i3 = { bar = "polybar", login_manager = "gdm"  } }
]

# ...etc

The following approach as several advantages :

• enable to write structured variables context for dotfiles template and eliminate some off the mental load currently required to remember which variables file is loaded were etc.
• Enable better templating experience

  .class {
      {%- if profiles is containing("fancy") -%}
      color: {{red}}
      {%- else -%}
      color: {{black}}
      {%- endif -%}
   }
  

• We could provide some default context like os, profiles, locale etc.