Draft: Proxy install events for Jira connect self-managed

What does this MR do and why?

This MR is to address the missing parts of #325282 (closed)

Once an installation is updated with a instance_url we will send a installed event webhook to the instance to pretend that the app was installed on Jira. Whenever we receive events for installations that have a instance_url we need to forward them to the instance.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.