Integrate OpenSSL 3.x

[pde-cds]

Created a buildable state including OpenSSL 3.0.12 and Apache Subversion 1.14.3. Currently only x64,x86 and ARM64 build sucessfully including Unittests (Some Unittest had to be deactivated because they relied on ctf.open.collab.net.) .Net Core 3.1 builds are also successful but UnitTests fail -> Maybe update to .Net 6.0 or higher?.NET 6.0 update seems to be more difficult as expected -> Staying on .NetCore3.1

Necessary steps

• [x] Alternative to svn co for OpenSSL because Github sunsetted the svn support -> using git clone for github based projects
• [x] Either make VSTest for Dotnet Core runnable again or upgrade to Dotnet 6.0 or higher -> Tests for .Net Core 3.1 do run but only on x64 because of https://github.com/actions/setup-dotnet/issues/485 Updated SharpSvn.Tests to net6.0 (build artifacts stay on .netcore3.1
• [ ] Check if patches of OpenSSL 1.1.x are also necessary for 3.x because they currently not integrated into the build

[rhuijben]

Feel free to update to .Net 6.

Talked with Markus. Feel free to get this through... I'll get things released through NuGet when done on master.

[rhuijben]

@pde-cds check your mail. Should be invite to project member, so the tests should work directly, etc.