Correctly set ExactArgs if generated command has positional arguments

[andrewnester]

Changes

Some of the command such as databricks alerts create require positional arguments which are not primitive.

Since these arguments are required, we should correctly set ExactArgs for such commands

Fixes #367

Tests

Running databricks alerts create

Before

andrew.nester@HFW9Y94129 cli % ./cli alerts create                     
panic: runtime error: index out of range [0] with length 0

goroutine 1 [running]:
github.com/databricks/bricks/cmd/workspace/alerts.glob..func1(0x22a1280?, {0x2321638, 0x0, 0x0?})
	github.com/databricks/bricks/cmd/workspace/alerts/alerts.go:57 +0x355
github.com/spf13/cobra.(*Command).execute(0x22a1280, {0x2321638, 0x0, 0x0})
	github.com/spf13/cobra@v1.7.0/command.go:940 +0x862
github.com/spf13/cobra.(*Command).ExecuteC(0x22a0700)
	github.com/spf13/cobra@v1.7.0/command.go:1068 +0x3bd
github.com/spf13/cobra.(*Command).ExecuteContextC(...)
	github.com/spf13/cobra@v1.7.0/command.go:1001
github.com/databricks/bricks/cmd/root.Execute()
	github.com/databricks/bricks/cmd/root/root.go:80 +0x6a
main.main()
	github.com/databricks/bricks/main.go:18 +0x17                                           

After

andrew.nester@HFW9Y94129 cli % ./cli alerts create                                                                
Error: provide command input in JSON format by specifying --json option

Acceptance test

=== RUN   TestAccAlertsCreateErrWhenNoArguments
    alerts_test.go:10: gcp
    helpers.go:147: Error running command: provide command input in JSON format by specifying --json option
--- PASS: TestAccAlertsCreateErrWhenNoArguments (1.99s)
PASS