[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#3166

X-original-commit: 12e1085199
Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

content/developer/howtos/rdtraining/02_setup.rst

@@ -248,10 +248,10 @@ Here are some useful Git commands for your day-to-day work.
   .. code-block:: console
 
      $ cd $HOME/src/odoo
-     $ git switch master
+     $ git switch {BRANCH}
 
      $ cd $HOME/src/enterprise
-     $ git switch master
+     $ git switch {BRANCH}
 
 - Fetch and rebase:
 
@@ -259,11 +259,11 @@ Here are some useful Git commands for your day-to-day work.
 
      $ cd $HOME/src/odoo
      $ git fetch --all --prune
-     $ git rebase --autostash odoo/master
+     $ git rebase --autostash odoo/{BRANCH}
 
      $ cd $HOME/src/enterprise
      $ git fetch --all --prune
-     $ git rebase --autostash enterprise/master
+     $ git rebase --autostash enterprise/{BRANCH}
 
 Code Editor
 -----------