Refactor New Objective form to be more generic

What does this MR do and why?

Refactor New Objective form to be more generic

Make the component more generic so we can reuse it for a New Epic form in a follow-up MR

No changelog as it is a refactor behind feature flag okrs_mvc

Issue: #392992 (closed)

Screenshots or screen recordings

No changes

Before	After

How to set up and validate locally

1. In rails console

   Feature.enable(:okrs_mvc)

2. Visit any issues list page such as http://127.0.0.1:3000/flightjs/flight/-/issues/
3. Click the toggle button next to New issue and select New objective
4. Confirm that creating an objective still works

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.