Support template keys in rule metadata inside rule templates

https://issues.jboss.org/browse/GUVNOR-1431 created support for the use of template keys in LHS and RHS expressions, but to be able to do the same for metadata would be very useful for us.
The rule template could look like this:
rule "xyz"
@Description(@

)
when
...
then
...
On load template data users can create rules including metadata