clean up, refactor, documentation

- reducing amount of splitting in configs
- documenting configuration

tasks/pkgs/rust.yml

@@ -2,9 +2,11 @@
 - ansible.builtin.include_vars:
     file: rust.yml
     name: _rust
+- ansible.builtin.set_fact:
+    pkgconfig.rust: "{{ _rust | ansible.builtin.combine(pkgconfig.rust) }}"
 
 - name: append to pkgs
   set_fact:
-    syspkgs: "{{ syspkgs + _rust[ansible_system].pkgs }}"
+    syspkgs: "{{ syspkgs + _rust.pkgs[ansible_system] }}"
   tags:
     - packages