[IMP] conf.py, *: interpolate the version and releases in the content

This commit replaces hard-coded occurrences of the version and of the
last, current and next releases' version with placeholders interpolated
at build time to avoid manually updating these after each freeze.

task-2917614

closes odoo/documentation#3170

X-original-commit: fa2d0f6363
Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

content/developer/reference/backend/module.rst

@@ -154,5 +154,4 @@ Available manifest fields are:
     Deprecated. Replaced by ``auto_install``.
 
 .. _semantic versioning: https://semver.org
-.. _existing categories:
-     https://github.com/odoo/odoo/blob/14.0/odoo/addons/base/data/ir_module_category_data.xml
+.. _existing categories: {GITHUB_PATH}/odoo/addons/base/data/ir_module_category_data.xml

content/developer/reference/backend/testing.rst

@@ -595,8 +595,8 @@ Javascript
 #. Add any step you want.
 
 Every step contains at least a trigger. You can either use the `predefined steps
-<https://github.com/odoo/odoo/blob/master/addons/web_tour/static/src/js/tour_step_utils.js>`_ or write
-your own personalized step.
+<{GITHUB_PATH}/addons/web_tour/static/src/js/tour_step_utils.js>`_ or write your own personalized
+step.
 
 Here are some example of steps: