[addon-knobs]: options knob with display: multi-select inferring wrong type info #20

Just copied from this very nice detailed explanation in storybookjs/storybook#10692

Until storybookjs/storybook#12561 is resolved, a fix for the type error should be added to v5 🙏

Describe the bug
When using the options knob with {display: multi-select}, it is inferring the return type from the values of the valuesObj, which need to be strings in order for the multi-select to work. The return type is being inferred as string when the multi-select actually returns an array of strings, so string[].

To Reproduce
Steps to reproduce the behavior:

1. Create a optionsKnob with the display set to multi-select
2. pass in a values object with the labels and values you expect to see in the dropdown.
3. pass in a default value, an array of the values you expect to be auto-selected.
4. check the return value that optionsKnob returns

Expected behavior
Given that the optionsKnob returns an array of strings when it is being used as a multi-select, it should return the correct type information: string[]

Screenshots
The implementation:

The resulting console log of what options is returning:

The type error:

The knob used in the UI is correct:

Code snippets

      const valueOptions = {
        facebook: "facebook",
        twitter: "twitter",
        email: "email",
        link: "link"
      };
      const defaultNetworks: string[] = [
        "facebook",
        "twitter",
        "email",
        "link"
      ];

      const networks: string[] = options( //should return an array of strings
        "Networks",
        valueOptions,
        defaultNetworks,
        {
          display: "multi-select"
        }
      );

System:

  System:
    OS: macOS 10.15.4
    CPU: (8) x64 Intel(R) Core(TM) i7-8559U CPU @ 2.70GHz
  Binaries:
    Node: 10.16.3 - /usr/local/bin/node
    Yarn: 1.22.4 - /usr/local/bin/yarn
    npm: 6.9.0 - /usr/local/bin/npm
  Browsers:
    Chrome: 81.0.4044.138
    Safari: 13.1
  npmPackages:
    @storybook/addon-actions: 5.3.10 => 5.3.10 
    @storybook/addon-docs: 5.3.10 => 5.3.10 
    @storybook/addon-info: 5.3.10 => 5.3.10 
    @storybook/addon-knobs: 5.3.10 => 5.3.10 
    @storybook/addon-links: 5.3.10 => 5.3.10 
    @storybook/addon-options: 5.3.10 => 5.3.10 
    @storybook/addon-storysource: ^5.3.13 => 5.3.18 
    @storybook/addons: 5.3.10 => 5.3.10 
    @storybook/react: 5.3.10 => 5.3.10