fix: Update MixPanel proxy URL

[NicholasEllul]

Description

This PR updates the MixPanel proxy URL to use the updated production server domain instead. We should no longer be using the dev server.

Related issues

No related issues.

Manual testing steps

1. You can test the proxy server is up by running the following command in your terminal (project token in invalid)

curl -i -s -k -X $'POST' \
    -H $'Host: proxy.api.cx.metamask.io' -H $'Accept: application/json' -H $'Content-Type: application/json' -H $'Content-Length: 30' \
    --data-binary $'{\"distinct_ids\": [\"12312312\"]}' \
    $'https://proxy.api.cx.metamask.io/mixpanel/v1/api/app/data-deletions/v3.0/?token=abcdefg'

2. In the MetaMask application, navigate Settings -> Security & Privacy -> Delete MetaMetrics Data. Upon clicking you should see a request made.

Screenshots/Recordings

Before

Not applicable

After

Not applicable

Pre-merge author checklist

• I’ve followed MetaMask Coding Standards.
• I've clearly explained what problem this PR is solving and how it is solved.
• I've included manual testing steps
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.
• I’ve properly set the pull request status:
  • In case it's not yet "ready for review", I've set it to "draft".
  • In case it's "ready for review", I've changed it from "draft" to "non-draft".

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (0b5d647) 40.66% compared to head (1bdc118) 40.67%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8517   +/-   ##
=======================================
  Coverage   40.66%   40.67%           
=======================================
  Files        1240     1240           
  Lines       30013    30010    -3     
  Branches     2870     2870           
=======================================
  Hits        12206    12206           
+ Misses      17109    17106    -3     
  Partials      698      698           

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[sonarqubecloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sethkfman]

LGTM

[github-actions]

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