[ADD] doc: database upgrade API: structure change
[ADD] doc: database upgrade API: structure change

1° add a second level of titles because they were too long and
overrided the second column (the 'code column)
2° Add 'double backticks' around some keys

dfang/odoo,hip-odoo/odoo,microcom/odoo,dfang/odoo,ygol/odoo,Elico-Corp/odoo_OCB,storm-computers/odoo,hip-odoo/odoo,syci/OCB,stephen144/odoo,bplancher/odoo,hip-odoo/odoo,sysadminmatmoz/OCB,bplancher/odoo,Elico-Corp/odoo_OCB,hip-odoo/odoo,optima-ict/odoo,syci/OCB,laslabs/odoo,storm-computers/odoo,microcom/odoo,optima-ict/odoo,bplancher/odoo,dfang/odoo,syci/OCB,stephen144/odoo,dfang/odoo,storm-computers/odoo,laslabs/odoo,laslabs/odoo,laslabs/odoo,optima-ict/odoo,Elico-Corp/odoo_OCB,Elico-Corp/odoo_OCB,Elico-Corp/odoo_OCB,sysadminmatmoz/OCB,optima-ict/odoo,sysadminmatmoz/OCB,syci/OCB,sysadminmatmoz/OCB,ygol/odoo,optima-ict/odoo,ygol/odoo,bplancher/odoo,dfang/odoo,syci/OCB,microcom/odoo,storm-computers/odoo,bplancher/odoo,storm-computers/odoo,stephen144/odoo,stephen144/odoo,ygol/odoo,microcom/odoo,sysadminmatmoz/OCB,sysadminmatmoz/OCB,hip-odoo/odoo,stephen144/odoo,optima-ict/odoo,microcom/odoo,ygol/odoo,bplancher/odoo,laslabs/odoo,dfang/odoo,syci/OCB,hip-odoo/odoo,Elico-Corp/odoo_OCB,microcom/odoo,sysadminmatmoz/OCB,storm-computers/odoo,laslabs/odoo,stephen144/odoo,ygol/odoo,ygol/odoo