Resolve "Free-text field for lab instructions"

What does this mr do?

Add a textfield to labs which allows the teachers and head ta's to add free text to

Screenshots

before

after

Teacher view: Studnet view:

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made.
• Tests were created to test the feature.
• I have updated the documentation accordingly.
• I adhere to the style guide. Closes #521 (closed)