Multiselect's value is an array of strings

[jasalisbury]

Description of change
The multiselect component used an array of objects for the value with the shape [{ label: ..., value: ... }]. This PR updates the value to be an array of strings.

Add testing library linter and fix all the violations.

I had a good fight getting the new linter to work in VS code. If you find eslint inside vs code no longer works after pulling this change down try to set

    "eslint.workingDirectories": [
        ".", "./frontend"
    ],

in your vscode settings.json file.

How to test

1. Pull down code, install dependencies
2. Fill out an activity report, make sure your console is open
3. Click submit, in your console any multiselect field should have a value like ["one", "two", ...], while previously the value would be [{label: "one", value: "one"}, ...]

Issue(s)

• Saving an Activity Report HHS/Head-Start-TTADP#98

Checklist

• [n/a] Meets issue criteria
• Code tested
• [n/a] Meets accessibility standards (WCAG 2.1 Levels A, AA)
• [n/a] Documentation updated
  • API methods
  • Boundary and Data Flow Diagrams
  • Architectural Decision Records written for major infrastructure decisions with the Nygard template
  • OSCAL templates completed when security controls are implemented or modified

[kryswisnaskas]

Looks good!