feat: add sections in task tab

[bharat-1809]

Description

This PR adds sections in the task tab of the relations page. To-do and achieved tasks are separated using an expandable panel.

Fixes #95

Flutter Channel:

• I have used the Flutter Beta channel on my local machine

Type of Change:

• Code

Code/Quality Assurance Only

• New feature (non-breaking change which adds functionality pre-approved by mentors)

How Has This Been Tested?

This is tested on a physical device.

Steps:

• Goto Relations Page
• Click on the Tasks Tab

Here is a working demo of the same

Checklist:

• My PR follows the style guidelines of this project
• I have performed a self-review of my own code or materials

Code/Quality Assurance Only

• My changes generate no new warnings

[techno-disaster]

LGTM

[techno-disaster]

@anitab-org/qa-team can someone test this?

[isabelcosta]

@bharat-1809 can you please fix the merge conflict here so we can review this again and merge once approved?

[bharat-1809]

@isabelcosta Sure!

[bharat-1809]

@isabelcosta I have resolved the conflicts!

[isabelcosta]

Looks good 👍

[isabelcosta]

@techno-disaster can you test this and show the proof here please :) If you feel this is working as expected then feel free to merge

[techno-disaster]

Ok, Ill test this. i guess i need to update docs on the artifacts thingy asap. https://github.com/anitab-org/mentorship-flutter/pull/130/checks

[robotjellyzone]

I have tested this pr and its working in the way it should 👍 .
The changes made in this PR were tested locally. Following are the results:

1. Code Review: Done

2. All possible responses were tested as below:
   Screenshot/gif:

Expected Result: adding sections in the task tab
Actual Result: Same as above

3. Additional testcases covered: n/a
4. Device : PIXEL XL API 27

[isabelcosta]

@robotjellyzone thank you so much for your help testing this PR 🙌