Improvements to kube-linter plugin (#1438)

- Lint the entire directory all at once
- If kube-linter exits with a "success" exit code but no stdout, treat
it as a Lint Error rather than invoking the parser (which would crash
due to trying to parse a blank string)

qlty-plugins/plugins/linters/kube-linter/plugin.toml

@@ -46,3 +46,5 @@ output = "stdout"
 output_format = "sarif"
 output_category = "vulnerability"
 output_level = "medium"
+missing_output_as_error = true
+target = { type = "literal", path = "." }