[FIX] packaging: allow install on fedora29

Fedora 29 switched to python 3.7. It seems that there is no official
way to build a RPM package that could works with 3.6 and 3.7.
Building two different packages for each version could open the pandora
box of packaging.

With this commit an ugly hack is used: if python3.7 is found, the odoo
directory is symlinked into its site-packages dir.

fixes #30579

closes odoo/odoo#30618

setup.cfg

@@ -9,7 +9,7 @@ requires =
   nodejs-less
   pychart
   pyparsing
-  python(abi) = 3.6
+  python(abi) >= 3.6
   python3-babel
   python3-decorator
   python3-docutils

setup/redhat/postinstall.sh

@@ -10,6 +10,12 @@ ODOO_LOG_DIR=/var/log/odoo
 ODOO_LOG_FILE=$ODOO_LOG_DIR/odoo-server.log
 ODOO_USER="odoo"
 
+if [ -d /usr/lib/python3.7 ]; then
+    SITE_PACK_DIR37=/usr/lib/python3.7/site-packages
+    [[ ! -d ${SITE_PACK_DIR37} ]] && mkdir -p ${SITE_PACK_DIR37}
+    ln -s /usr/lib/python3.6/site-packages/odoo ${SITE_PACK_DIR37}/odoo
+fi
+
 if ! getent passwd | grep -q "^odoo:"; then
     groupadd $ODOO_GROUP
     adduser --system --no-create-home $ODOO_USER -g $ODOO_GROUP