[sitecore-jss-react] Preserve form state and interactivity between rerenders

[yavorsk]

• This PR follows the Contribution Guide
• Changelog updated
• Upgrade guide entry added

Description / Motivation

Using dangerouslySetInnerHTML caused scripts to execute only on the initial render. Subsequent re-renders would update the HTML but would not re-trigger executeScripts, breaking form validation and interactive features.
Avoid this by replacing dangerouslySetInnerHTML with setting innerHtml offormRef.
Decoupled logic into two distinct useEffects: one for fetching content and one for injecting HTML/executing scripts.

• Form scripts now run correctly on every re-render.
• Form state is now preserved across renders.

Testing Details

• Unit Test Added
• Manual Test/Other (Please elaborate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

[illiakovalenko]

👍