Update introcourse module 5, add worked solution and link to updated example application.

[thestokkan]

Add 'previous' and 'next' links, format knowledge check as dropdowns with answers

Update first two tasks, include detailed solution

Update validation task, add worked solution

Add worked solution for custom confirmation page text.

Description

Related Issue(s)

• Update Introcourse module 5 #1177

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)
• All tests run green

Documentation

• User documentation is updated with a separate linked PR in altinn-studio-docs. (if applicable)