feat(CE): Added Mixpanel Destination Connector

[xyfer17]

Description

• Add Mixpanel Destination Connector
• Add Unit Test for Mixpanel Connector

Related Issue

Relates to issue #396 Mixpanel: Destination Connector

Type of Change

• New feature (non-breaking change which adds functionality)
• New Connector (Destination or Source Connector)
• Refactoring
• Bug fix (non-breaking change which fixes an issue)
• Styling change
• Breaking change (fix or feature that would impact existing functionality)
• Documentation update
• Chore

How Has This Been Tested?

Checklist:

• Added unit tests for the changes made (if required)
• Ensure a branch name is prefixed with feature, bugfix, hotfix, release, style or chore followed by / and branch name e.g feature/add-salesforce-connector
• Have you made sure the commit messages meets the guidelines?
• Added relevant screenshots for the changes
• Have you tested the changes on local/staging?
• Added the new connector in rollout.rb
• Have you updated the version number of the gem?
• Have you ensured that your changes for new connector are documented in the docs repo or relevant documentation files?
• Have you updated the run time dependency in multiwoven-integrations.gemspec if new gems are added
• Have you made sure the code you have written follows the best practises to the best of your knowledge?

[TivonB-AI2]

@xyfer17 Is it possible to use Multiwoven::Integrations::Core::HttpClient.request for sending a request? Look at http destination connector for reference