Update nuget packages to use license instead of licenseUrl

[tsimbalar]

CI builds of Serilog.Sinks.Console and Serilog.Settings.Configuration print out a warning message here and there :

NU5125: The 'licenseUrl' element will be deprecated. Consider using the 'license' element instead.

Based on announcement by the Nuget team :

'licenseUrl' as package metadata is now deprecated, use 'license' instead

Based on the Nuget documentation, we should therefore start changing all the Nuget package metadata of all the Serilog projects toward this new format :

<license type="expression">Apache-2.0</license>

or in a .csproj file (see docs) :

<PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>

This will reference the Apache 2.0 license, the license that is used across the "official" Serilog repos.

Because it is a change across many repos, and does not have a high priority, I think it makes sense to apply the change little by little, as we release new versions of the sinks and other Serilog extensions.

[tsimbalar]

There was a comment in serilog/serilog-settings-configuration#158 (comment) about whether we should maybe use license file instead (i.e. include a file containing the license as part of the nuget package, and point to that file).

I think it's better to be consistent across the Serilog repos, so I'd let @nblumhardt give his opinion, and go in that direction :)

Nick, any opinion on the topic ? Should we use :

1. license expression = Apache v2.0
2. license file = our LICENSE file in every repo (which is a copy of the Apache v2.0 license I believe)

[nblumhardt]

Hi @tsimbalar - thanks for the heads-up. I didn't notice that including the license file was an option; I can see some benefits to both techniques. The license file is probably the more defensive option and I'd go with that if the effort is the same in both cases. (Using the expression is also completely fine, though, and might have the advantage of being easier to browse in the NuGet.org UI.)

[nblumhardt]

Shipped in 2.9.0-dev-*