[5.x] Add blueprint repository hook

[simonerd]

We are exploring ways to reuse one blueprint in multiple collections to allow us to split up (otherwise identical) content into more collections for better performance, permission-control and usability. We want to avoid copy-pasting the blueprint file.

This PR introduces a hook to the makeBlueprintFromFile function in the BlueprintRepository. This would allow to change the path of the blueprint file and therefore use a different blueprint for an entry than its actually intended one.

Example

Say I have a collection pages with a blueprint page. I now need another collection subpages where the blueprint page should actually be identical with the one from pages. I can now add a hook like this:

Blueprint::hook('makeFromFile', function ($payload, $next) {
    if ($payload->namespace === "collections/subpages") {
        $payload->namespace = "collections/pages";
        $payload->path = str_replace("subpages/page.yaml", "pages/page.yaml", $payload->path);
    }

    return $next($payload);
});

What do you think?

[simonerd]

I realised that I should be able to use the EntryBlueprintFound event to achieve the same without an additional hook. Yeah I know, it's almost like there's someone in the core team that constantly reminds us to read the flippin manual. Closing this for now.