Webhooks: Add webhook endpoint ping test button in Create Webhook modal

[mxllv]

Problem

Developers save invalid or unreachable webhook URLs without verifying connection first.

Acceptance Criteria

• Add 'Test Connection' button in Webhook Configuration modal.
• Send ping event payload to specified URL.
• Display HTTP response status code and latency.

[alexatsejames-alt]

@alexatsejames-alt has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer, can you pls assign these issue to me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @alexatsejames-alt to this issue.