Adding workflow execTimeout and keepActive properties (#223)

* Adding execTimeout property to top-level workflow props

Signed-off-by: Tihomir Surdilovic <[email protected]>

* update and added use case example

Signed-off-by: Tihomir Surdilovic <[email protected]>

* fix for workflow schema

Signed-off-by: Tihomir Surdilovic <[email protected]>

* change to execTimeout and recommendation fixes

Signed-off-by: Tihomir Surdilovic <[email protected]>

* adding core concepts section and adding adhoc to start defs

Signed-off-by: Tihomir Surdilovic <[email protected]>

* small fixes

Signed-off-by: Tihomir Surdilovic <[email protected]>

* more updates to spec doc

Signed-off-by: Tihomir Surdilovic <[email protected]>

* small fixes

Signed-off-by: Tihomir Surdilovic <[email protected]>

* fix adhoc doc

Signed-off-by: Tihomir Surdilovic <[email protected]>

* adding examples and update to spec doc

Signed-off-by: Tihomir Surdilovic <[email protected]>

Author: Tihomir Surdilovic