Update description when editing iteration

What does this MR do?

Fix a small bug when editing the description of iterations.

When changing the description an iteration, update the desriptionHtml so the description is updated.

Before	After
Screen_Recording_2020-09-08_at_7.23.48_pm	Screen_Recording_2020-09-08_at_7.20.54_pm

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Merge request performance guidelines
• Style guides