Split plugin running (#91)

* begin plugin test

* add first test for plugin provider

* add step schema

* provide deploy stage input

* fix running stage input

* add test using docker deployer

* add thoughts on testing

* add stack to track history

* test happy path stage history

* add parallel test

* increase coverage of errors

* cover wrong stage and steps

* add lifecycle test

* update test

* call OnStageChange in concurrency safe sections

* add deploy failure test

* add run fail test

* remove dead code in tests

* add start stage

* fix stashed code

* fix plugin provider lifecycle stages

* remove stack and refactor tests

* remove dead code

* remove comment

* remove engine test

* edit test

* edit engine test

* remove stage changes in provide stage input to fix bug in executor notify steps

* fix linting errors

* remove dead code

* add more comments

* change deploy next stage

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Co-authored-by: Dustin Black <[email protected]>