Scheduler trigger interval as environment variable setting

[PopaRares]

Description

Added a new setting called SCHEDULER_TRIGGER_INTERVAL that sets the LoopTimeTrigger's sleep time between scheduler calls. Value is of type float. Default value is kept at 10 seconds.
Example call:

 SCHEDULER_TRIGGER_INTERVAL=3 ./scripts/dev.sh

How Has This Been Tested?

Set the SCHEDULER_TRIGGER_INTERVAL to some numerical value (default value is 10 seconds).

SCHEDULER_TRIGGER_INTERVAL=3.5 ./scripts/dev.sh

Checklist

• The PR is tagged with proper labels (bug, enhancement, feature, documentation)
• I have performed a self-review of my own code
• I have added unit tests that prove my fix is effective or that my feature works
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

cc:
@adelcast
@hugabora

[PopaRares]

@wangxiaoyou1993 I've been looking at the classes LoopTimeTrigger and TimeTrigger and I have some light concerns. Should the trigger_interval property be held in the TimeTrigger class? How things work currently is that LoopTimeTrigger does the waiting and TimeTrigger triggers the scheduler; going by that logic, the trigger_interval property should be a property of the entity that does the actual waiting: LoopTimeTrigger. Expandig from this, what are the advantages of having LoopTimeTrigger and TimeTrigger be 2 separate classes? TimeTrigger is only used with the loop part attached so maybe a good solution would be to merge these two? Let me know what you guys think!

[wangxiaoyou1993]

@wangxiaoyou1993 I've been looking at the classes LoopTimeTrigger and TimeTrigger and I have some light concerns. Should the trigger_interval property be held in the TimeTrigger class? How things work currently is that LoopTimeTrigger does the waiting and TimeTrigger triggers the scheduler; going by that logic, the trigger_interval property should be a property of the entity that does the actual waiting: LoopTimeTrigger. Expandig from this, what are the advantages of having LoopTimeTrigger and TimeTrigger be 2 separate classes? TimeTrigger is only used with the loop part attached so maybe a good solution would be to merge these two? Let me know what you guys think!

class LoopTimeTrigger inherits the class TimeTrigger. It's just one way to implement the time trigger. It's just to make it extensible if we want to add another implementation for TimeTrigger in the future.