[Workspace] Address UI issues of index patterns

[Kapian1234]

Description

Adjust the padding of index-pattern list panel to 16px.
Make the Pattern column bold, and the Data-source-connection column not bold
Ajust the spacing within the index-pattern detail panel to 16px
Add plusInCircle icon to the Add-scripted-field button
Ajust the space between the search bar and the button to 8px at Source-filters panel

Issues Resolved

Screenshot

Testing the changes

Changelog

• fix: Address UI issues of index patterns

Check List

• All tests pass
  • yarn test:jest
  • yarn test:jest_integration
• New functionality includes testing.
• New functionality has been documented.
• Update CHANGELOG.md
• Commits are signed per the DCO using --signoff

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 64.14%. Comparing base (636f399) to head (e6d5d66).
Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8287      +/-   ##
==========================================
+ Coverage   64.05%   64.14%   +0.08%     
==========================================
  Files        3741     3743       +2     
  Lines       88683    88833     +150     
  Branches    13817    13852      +35     
==========================================
+ Hits        56809    56980     +171     
+ Misses      31262    31238      -24     
- Partials      612      615       +3     

Flag	Coverage Δ
Linux_1	30.07% <ø> (+0.01%)	⬆️
Linux_2	58.86% <ø> (+<0.01%)	⬆️
Linux_3	40.36% <ø> (?)
Linux_4	31.58% <ø> (+0.14%)	⬆️
Windows_1	30.08% <ø> (+0.01%)	⬆️
Windows_2	58.81% <ø> (+<0.01%)	⬆️
Windows_3	40.36% <ø> (+0.01%)	⬆️
Windows_4	31.58% <ø> (+0.14%)	⬆️

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