Unit test example for WorkItemFormGroup

[h2floh]

Hi,

main purpose of this PR:

Include a minimal viable unit test example for React/TS components to the WorkItemFormGroup

• npm audit fix all security vulnerabilities
• bumping TS to v3.9
• bumping Webpack to v7
• bumping Node.JS in pipeline to v10.19 (LTS)
• adding minimal mocks for azure-devops-extension-sdk
• adding mocks for sample extension features
• adding unit tests for WorkItemFormGroupComponent to achieve 100% code coverage
• renaming WorkItemFormGroup manifest and html file, otherwise React testing lib will fail to import the component
• including unit test run into compile scripts
• adding jest/ts-jest configuration to package.json
• validated that sample extension package can be deployed to Visual Studio Marketplace, shared and installed and working
• validated that build pipeline successfully completes
• updated README.md to reflect that WorkItemFormGroup sample includes unit tests

Additional Azure DevOps Extension unit test samples can be found here:
https://github.com/h2floh/azure-dev-ops-react-ui-unit-testing