Implement a new policy check workflow (#1317)

* Adding policy_check support into yaml config

* Added policy check model and runtime structs

* Adding BuildPolicyCheckCommand to ProjectCommandBuilder

* Return incorrectly deleted code

* Remove BuildAutoPolicyPlanCommand from ProjectCommandBuilder

* Split runAutoCommand into two functions

runAutoPlanCommand - does what originally RunAutoplancommand was doing
except now it returns CommandResult and []models.ProjectCommandContext
runAutoPolicyCheckCommand - accepts CommandContext, CommandResult, and
[]models.ProjectCommandContext as arguments and runs PolicyCheckStep runner

* Refactor RunCommentCommand
* Remove BuildPolicyCheckCommand and rename StepCmdExec back to TerraformExec
* Add policy step runner logic and conftest interfaces.
* Add show step runner to policy check stage.

* Adding models.PolicyCheckCommand to buildCtx

This also means buildPlanAllCommands call buildCtx twice once with
models.PlanCommand and once with models.PolicyCheckCommand

* Adding new project_command_builder that supports policy_check

* Refactoring PolicyCheck specific logic into a PolicyCheckProjectCommandBuilder

* Moving events.CommandContext to models.CommandContext this will allow me
to remove buildCtx method and move ProjectCommandContext creation into
models package

* Policy Owners might be different types, for that reason we are
refactoring Owners into its own struct with specific keys defining
different owner types

Co-authored-by: Nish Krishnan <nishk@lyft.com>
Co-authored-by: Nish Krishnan <nishkrishnan@users.noreply.github.com>

cmd/server_test.go

@@ -100,6 +100,7 @@ var testFlags = map[string]interface{}{
 	VCSStatusName:              "my-status",
 	WriteGitCredsFlag:          true,
 	DisableAutoplanFlag:        true,
+	EnablePolicyChecksFlag:     false,
 }
 
 func TestExecute_Defaults(t *testing.T) {