Refactor Timeline Event Form

What does this MR do and why?

Timeline Event form was using an input within DatePicker unnecessarily, this is removed now and props updated appropriately.

The only other change made here is to move the style wrapping the timeline form to create_timeline_event so that timeline_events_form only contains the form making it easier to style when it will be reused for edit_timeline_event

This MR is part of a series of 5 MRs:

graph TD;
A[Add Edit Timeline Event Functionality] --> B[Refactor Timeline Event Form];
A[Add Edit Timeline Event Functionality] --> C[Refactor timeline event list];
A[Add Edit Timeline Event Functionality] --> D[Refactor timeline events list tests];
B[Refactor Timeline Event Form] --> E[Split Create timeline event from Timeline Event form];

The links are:

• Add Edit Timeline Event Functionality !95061 (merged)
• Refactor Timeline Event Form !94899 (merged) (you are here)
• Refactor timeline event list !95073 (merged)
• Refactor timeline events list tests !95046 (merged)
• Split Create timeline event from Timeline Event form !93545 (merged)

Screenshots or screen recordings

	before	after
without events
with events

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Within a project on the left hand menu bar navigate to Monitor > Incidents
2. Open an incident (create one if needed)
3. Using the tab headings, select Timeline
4. Create a timeline entry if there isnt one
5. On the right hand side of the timeline event select edit from the more options symbol

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #344060 (closed)