Execute chained workflow conditionally

Description of the feature request

Let a chained workflow be executed conditionally

Use case / for what or how I would use it

Since we don’t have yet selective builds for bitbucket, my use case is this:
I need to validate if contents in my mobile client folder has changes and set a env variable value for that.
Chained workflows should execute, or not, if this variable has the correct value. this way I dont have to specify the run_if statement for every step. Instead I would have in my .yaml file something like this:

   run_if: my_condition
        - step1

i think this would be helpful in other use cases with chained workflows or parallel execution when it is finally implemented

Thanks for the #feature-request @jmunoz!