Make it possible to disable Examine indexes by composition

[kjac]

Prerequisites

• I have added steps to test this contribution in the description below

Description

The upcoming search abstraction layer will need to work as an add-on to V16. For this to happen, we need to be able to disable the current Examine indexes, to let the search abstraction take over.

This PR moves the Examine DI setup to a composer, because composers can be omitted by code 😄

Testing this PR

First and foremost, make sure Examine still works as per usual - that is, indexing and search still works.

Now add a new composer which disables the AddExamineComposer of this PR. Something along these lines:

using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Infrastructure.Examine;

namespace Umbraco.Cms.Web.UI.Custom.Search;

[Disable(typeof(AddExamineComposer))]
public class DisableExamineComposer : IComposer
{
    public void Compose(IUmbracoBuilder builder)
    {
    }
}

Restart Umbraco. The Examine indexes should no longer appear in the Examine Management dashboard.

[Migaroez]

Works as advertised 🚀