Update template metadata for net8.0

[phenning]

Describe the bug

Create new project with NET 8 SDK, net7.0 project is created instead

To Reproduce

Install net8 SDK.
dotnet new console

Exceptions (if any)

None

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[phenning]

Following updates are needed:

1. Update template.json metadata to increment precedence, identity as appropriate
2. Update template.json Framework Symbol from net7.0 to net8.0
3. Update csproj/vbproj/fsproj TargetFrameworks from net7.0 to net8.0
4. Update template_feed/Microsoft.DotNet.Common.ProjectTemplates.7.0/Microsoft.DotNet.Common.ProjectTemplates.7.0.csproj identity to be 8.0

There are probably some other build infrastructure things that needs to be updated as well to make sure we are generating the correct packages and versions, but 1-3 should cover the actual template updates.

[phenning]

dotnet/installer#14953

[vlada-shubina]

@phenning the PR is already on: #27486 - we are waiting for test infrastructure to be ready to build .net 8 projects.

[kasperk81]

latest daily build (8.0.100-alpha.1.22607.6) still creates net7.0 csproj with dotnet new console. is it expected?