fix: only send sensor start event on first poke

[Mryashbhardwaj]

Is your feature request related to a problem? Please describe.
The existing sensor metric "sensor_start_event" call back gets invoked on every sensor poke.
This results in redundant database calls on optimus server. To overcome this we need to have some sort of stateful storage that can limit the "sensor_start_event" to only once per sensor attempt.

Describe the solution you'd like
It's ideal to use the XCOMs as a state storage for maintaining the record of events pushed per sensor attempt.
Before pushing the event to optimus the scheduler can check if a start event has already been sent

Describe alternatives you've considered

1. Reading the state of job run from the optimus server itself
2. keeping a cache at optimus

[coveralls]

Pull Request Test Coverage Report for Build 3836134017

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 91.609%

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Totals
Change from base Build 3828391416:	0.02%
Covered Lines:	8275
Relevant Lines:	9033

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💛 - Coveralls