Add an option to disable the UmbracoFile sink when using another sink

[Nikkelmann]

Currently when setting up serilog with another sink in the json configuration, Umbraco still adds the UmbracoFile "sink".
I would have expected that it would only add this sink, if no other sink was found.

Loggin to the json files on disk also causes a problem when publishing via Web Deploy, since the files are locked and cannot be deleted (which in it self is also an issue, since we kinda want to keep the log).

In my case I've setup the log with elastic search as such:

{
    "Serilog": {
        "Using": [
            "Serilog.Sinks.Elasticsearch"
        ],
        "MinimumLevel": {
            "Default": "Information"
        },
        "WriteTo": [
            {
                "Name": "Elasticsearch",
                "Args": {
                    "...": "...",
                    "typeName": "_doc",
                    "batchAction": "Create",
                    "emitEventFailure": "WriteToSelfLog",
                    "autoRegisterTemplate": false,
                    "customFormatter": "Serilog.Formatting.Elasticsearch.ElasticsearchJsonFormatter, Serilog.Formatting.Elasticsearch"
                }
            }
        ]
    }
}

Looking through the source code it seems like the only option is to add a flag, that tells the AddLogger to not setup the UmbracoFile sink:

Umbraco-CMS/src/Umbraco.Web.Common/Extensions/ServiceCollectionExtensions.cs

Line 80 in 9326cc5

public static IServiceCollection AddLogger(