Fix failed Jest tests & add notes to README

[mgratch]

The purpose of this PR is to fix the handling of team settings upon switching teams and to improve the robustness of the team configuration feature.

Acceptance Criteria

• The ConfigureHelpDesk function in the ConfigureIntegration.js file has been updated to handle default cases better, ensuring the correct helpdesk name is returned.
• A check has been added to confirm if the provided helpDesk value exists in HelpDeskConfigs, throwing an error if it doesn't.
• The ConfigureHelpDesk component now handles default values more gracefully by using JavaScript optional chaining and default values.
• Updates have been made to the TeamsList.js file to handle cases where team id and helpdesk values might be undefined.
• Jest snapshot test names have been updated to reflect the changed component names.
• The structure of the jest snapshot tests have been updated to match the new structure of the components.
• The README is updated to provide clarity on adding new tests and fix failed tests.

Testing

1. Checkout the fix-failed-tests branch
2. Run yarn test
3. Verify the tests all pass as expected.
4. Read the new sections of the README file and verify that it makes sense and makes it easier for a new developer to be able to start add / fixing tests.

[zackkatz]

Run the following command in your terminal: yarn test -- -u

@mgratch I ran that after running yarn build and all sorts of other commands and ran into a failed test.

Note: If you are using yarn test --watch, you are given the option to press u to update the snapshots.

I was not given the option to press u: