Move .NET Docker projects to .NET 8.0 TFM

[lbussell]

Here's a search query that should return all instances of the net7.0 TFM in our repos: https://github.com/search?q=net7.0+repo%3Adotnet%2Fdotnet-docker+OR+repo%3Adotnet%2Fdocker-tools+OR+repo%3Adotnet%2Fdotnet-buildtools-prereqs-docker+OR+repo%3Amicrosoft%2Fdotnet-framework-docker++path%3A*.csproj&type=code

.NET Docker

• [x] update-dependencies
• [x] update-dependencies Dockerfile
• [x] Microsoft.DotNet.Docker.Tests

Docker tools

• [x] file-pusher
• [x] file-pusher Dockerfile
• [x] yaml-updater
• [x] yaml-updater Dockerfile
• [x] ImageBuilder
• [x] ImageBuilder Dockerfile
• [x] ImageBuilder Tests

[lbussell]

[Triage] This is completed with the above referenced PRs.