cli/command/plugin: fix linting issues, and assorted cleanups

- fix various unhandled errors
- remove some locally defined option-types in favor of option-types
  defined by the client / api
- don't use unkeyed structs in tests, and add docs for some subtests
- fix some values in tests that triggered "spellcheck" warnings
- inline vars / functions that only had a single use.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/plugin/enable_test.go

@@ -48,7 +48,7 @@ func TestPluginEnableErrors(t *testing.T) {
 		}))
 		cmd.SetArgs(tc.args)
 		for key, value := range tc.flags {
-			cmd.Flags().Set(key, value)
+			assert.NilError(t, cmd.Flags().Set(key, value))
 		}
 		cmd.SetOut(io.Discard)
 		cmd.SetErr(io.Discard)