Modifying default variables and config

Renamed variables for defaults:
- flatpak_method -> default_flatpak_method: system
- defaults.paths.prefix -> default_install_prefix: /usr/local
New variables:
- default_install_method: package

tasks/helpers/go.yml

@@ -0,0 +1,9 @@
+# vim: set filetype=yaml.ansible :
+---
+- name: Install go package {{ pkg }}
+  become: "{{ ext_become }}"
+  environment:
+    GOBIN: "{{ path.bin }}"
+    PATH: "{{ path.go }}/bin:$PATH"
+  ansible.builtin.command:
+    cmd: go install {{ pkg }}