Move to .NET 6.0 and upgrade dependencies.

[EraYaN]

Also adds some extra conflict resolution to the program. Repos overwrite one another in the order that they are given, so the first repo is the most important etc.

This is a bit of a WIP, that Ours resolution probably need to be a command line argument.

[mpdeimos]

Hey, sorry for not coming back to your PR earlier. I was quite surprised that someone found this little tool and put some further effort into it. Thanks. However, as this was more like a one-off tool I totally forgot about the open PR here.

I skimmed over all the changes and I fear I have to read into my own code 1st again. It's been quite a while since I wrote all the things. I'd also target .NET 6 now.

What's also interesting for me: did you accomplish your task with the tool?

[EraYaN]

We did and we still use it every now and then, I'll check back on Monday I might have been targeting .NET 6 locally for a while, since I don't think I have .NET 5 install on my work machine anymore. I should also cleanup the launchSettings I guess.

[EraYaN]

Alright, so we did move it to .NET 6. The biggest downside is that the LibGit2Sharp project is very slow (and almost maintainer less) there is a non alpha version of the native binaries now, but no corresponding .NET library release, so essentially you'd need to wait for libgit2/libgit2sharp#1957 to upgrade the actual LibGit2Sharp release to some non-prerelease version.