[sitecore-jss-nextjs] Use correct placeholder ID format for dynamic placeholders metadata

[art-alexeyenko]

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

Description / Motivation

Short follow up to Placeholder Metadata work. We need to ensure rendering uid is being used in editing markup for dynamic placeholders.

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]

@art-alexeyenko These tests should be updated as well:
https://github.com/Sitecore/jss/blob/dev/packages/sitecore-jss-react/src/enhancers/withPlaceholder.test.tsx#L384-L417
https://github.com/Sitecore/jss/blob/dev/packages/sitecore-jss-react/src/components/Placeholder.test.tsx#L880-L907

[addy-pathania]

Please add/update unit tests.
Update changelog.

[addy-pathania]

Looks good