For this PR

This PR enables addons to supply predefined blueprints for existing collections.

Problem
Statamic previously introduced addon blueprint loading support (see #9324), but it was limited to top-level blueprints only. It did not allow addons to add blueprints to existing collections—for example, adding an extra blueprint to the "pages" collection to support features like a page builder with addon-provided and autoloaded fieldsets.

Solution
This PR extends the blueprint loading mechanism, enabling addons to load entry blueprints for any existing collection. To make use of this functionality, addons must follow this directory structure:

Addon Root
└── resources/
    └── blueprints/
        └── collections/
            └── {collection-handle}/
                └── {blueprint-name}.yaml

Which will result in the addon blueprints being visible and selectable for that collections entries.