Add a new ViewsReferenceSetting plugin to allow per paragraph handling of the grid settings.

Problem/Motivation

When embedding a View via the Views Reference field (commonly on a Paragraph type), site builders cannot adjust views_bootstrap grid-related options (e.g., columns per breakpoint, gutter/row behavior) per instance. Today this forces duplication of Views displays just to vary grid settings by context, increasing maintenance overhead and limiting flexibility.

It would be useful if views_bootstrap exposed a ViewsReferenceSetting plugin so editors can override grid settings per referenced View instance, similar to how other modules integrate with Views Reference. Reference implementation pattern: viewsreference/src/Plugin/ViewsReferenceSetting.

Steps to reproduce

1. Create a Paragraph type with a Views Reference field.
2. Create a View that uses a Views Bootstrap grid style (e.g., Grid/Cards) with specific column settings.
3. Add two Paragraphs referencing the same View where each context needs different grid columns (e.g., 2-col vs 4-col at md).
4. Observe: there is no per-reference UI to change the grid; you must duplicate the View/display to achieve different grids.

Proposed resolution

• Add a ViewsReferenceSetting plugin in views_bootstrap to expose grid-related options on the Views Reference widget/form, enabling per-entity overrides.
• Initial options to expose (subject to maintainer feedback):
  • Columns per breakpoint (e.g., xs/sm/md/lg/xl/xxl or Bootstrap row-cols equivalents).
  • Gutter/row behavior (where applicable).
  • Optional flags such as equal height/stacking if provided by the chosen style plugin.
• Implementation sketch:
  • Create plugin class under Plugin/ViewsReferenceSetting/BootstrapGrid.php (or per-style variants) that reads/writes the style options and applies them via the Views Reference settings alter hook.

Remaining tasks

• Confirm the exact set of grid options that should be overrideable per reference.
• Implement the ViewsReferenceSetting plugin(s) with form elements and value mapping to the style plugin options.
• Add automated tests (kernel/unit) to verify option persistence and runtime application.
• Update documentation with usage examples and screenshots.
• Changelog entry and release note.

User interface changes

• New settings section on the Views Reference widget/edit form exposing grid controls (visible only when the referenced display uses a views_bootstrap grid style).

API changes

• New ViewsReferenceSetting plugin class(es) provided by views_bootstrap; no breaking changes to existing APIs.

Data model changes

• No changes required — settings schema for ViewsReferenceSetting plugins is handled by the viewsreference module.