Replace m UI popover with studio popover in mergeconflict warning

[ghost]

Description

• Replacing the MUI Popover with StudioPopover in DownloadRepo and MergeConflictWarning for Merge conflict page
• Replacing h tags with Heading component from the designsystem
• Replacing p tags with Paragraph component from the designsystem
• Adding CSS variables

Related Issue(s)

• The PR itself

Verification

• [x] Your code builds clean without any errors or warnings
• [x] Manual testing done (required)
• [x] Relevant automated test added (if you find this hard, leave it and we'll help out)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 91.05%. Comparing base (c91bfd7) to head (15796e3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #12907 +/- ## ======================================= Coverage 91.04% 91.05% ======================================= Files 1387 1389 +2 Lines 19698 19697 -1 Branches 2387 2386 -1 ======================================= + Hits 17934 17935 +1 + Misses 1501 1500 -1 + Partials 263 262 -1 ```

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