[E & A] Implement redesigned timeline handles and labels

[hanbyul-here]

Implementation ticket of

• Revisit layer groups / datasets #774

Warning

Hold for now until the design is finished

Refinement required

• Clarification on the timeline needed
• The details of the design can be changed. Check the Figma link to see the latest design.

Figma Link: https://www.figma.com/file/9INQauBWhiRxvOWDGhRrxO/US-GHG-Center?type=design&node-id=703%3A926&mode=design&t=Jc1CpvnWiVIwmbr8-1

Acceptance criteria

• Style change of timeline handles
• Implementation of the new side handles that allow users to adjust the start and end dates

[faustoperez]

Design ticket here 👉 #833

[sandrahoang686]

Looked into code to help gauge effort here. This looks to be mostly css / stylistic changes. I estimate effort to be ~ 1-2 days likely. Changes would happen in /exploration/components/timeline/timeline-head.tsx file.

[faustoperez]

This looks to be mostly css / stylistic changes

This is still WIP but I'll try to keep it that way.

[aboydnw]

I didn't catch this one before making #979
I'm going to close this on as a duplicate