chore: make testing distributed header injection easier in Example app

[ganeshnj]

What and why?

Testing multiple header types and injection control is not one click away.

I'm not a SwiftUI expert, the MultiSelector code is inspired from https://github.com/Jeehut/MultiSelectorDemo/tree/main

How?

This code was in my stashes for some time and it makes sense to add to our manual testing to help everyone.

• Add support injection types
• Ability to select multiple headers
• Print JSON response for quick verification
• Changed default address to https://httpbin.org/get which returns back the headers which we can quickly verify.

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference
• Add CHANGELOG entry for user facing changes

Custom CI job configuration (optional)

• Run unit tests for Session Replay

[ncreated]

Nice 👌