Add option to toggle the snippet admin to a list per snippet type

[wimvds]

Added a config toggle to switch between the single snippet list view (current) and a list view per snippet type (with a navigation entry per snippet type in the admin sidebar).

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Fixed tickets
Related issues/PRs	#4278
License	MIT
Documentation PR	sulu/sulu-docs#

What's in this PR?

A config toggle to switch between the single snippet list view (current) and a list view per snippet type (with a navigation entry per snippet type in the admin sidebar) has been added to the Sulu snippet configuration.

Why?

The single list of snippets becomes a burden when you have a few snippet types with a lot of content, it's easier to manage the snippet types separately.

Example Usage

The default admin view for the snippets is the current single list view. To toggle to the new view (with subnavigation per snippet type) you should have the following in your configuration :

sulu_snippet:
    admin_view: types_list

To revert back either remove the admin_view or set it's value to single_list.

A screenshot of the admin when the new view is active :

To Do

• Create a documentation PR

[wimvds]

I just realized that this can also be done by decorating the StructureFormMetadataLoader and replacing the AdminSnippet service via Symfony configuration... So maybe I could just document how to do that instead (though it's not 100% future proof of course - as it depends on the StructureFormMetadataLoader not changing ;p).

[alexander-schranz]

@wimvds Nice work, we need to discuss also with the UX team in which direction we want to go here. Thank you already for the work and implementation you provided.

[mario-fehr]

How about a tabview like in the ArticleBundle?

[mamazu]

Voting all for it, but I think the tabview could be a problem if you have a lot of snippet types.

[alexander-schranz]

Think this is something we could discuss again when we now rewrite the articles and snippets based on Content Bundle. To think what is best or if we want to have possibility todo it by config or not.