Split errors in Tool check

[chshersh]

Currently, the checkTool function has the following type:

checkTool :: cmd -> Tool cmd -> IO ToolCheckResult

where ToolCheckResult is defined as follows:

data ToolCheckResult
    = ToolNotFound Text
    | ToolWrongVersion Text
    | ToolOk

A value of ToolCheckResult is thrown as an exception here:

iris/src/Iris/Env.hs

Lines 138 to 141 in 6be65d4

	for_ cliEnvSettingsRequiredTools $ \tool ->
	checkTool cmd tool >>= \case
	ToolOk -> pure ()
	toolErr -> throwIO $ CliEnvException $ CliEnvToolError toolErr

This is suboptimal because the result can never have the ToolOk constructors but we're forcing downstream users to handle this case.

So we want to split success and error cases in the ToolCheckResult type.