Revive "Timer and calendar rule attributes is in DRL" section

Issue Description:

In the current docs (8.30.0.Final), "Timer and calendar rule attributes in DRL" section is commented out in _drl-rules.adoc because it may not be meaningful with Kogito use cases. However, it's meaningful with pure Drools.

In addition, "Rule attributes" table tells wrong information about `int` (interval), that should be `int` (initialDelay interval).

Acceptance Criteria:

"Timer and calendar rule attributes is in DRL" section is rendered. "Rule attributes" table is fixed.