Update e2e tests and e2e test infrastructure

[IvanZosimov]

Description:
In the scope of this PR, the following changes were made:

1. The code of the verify-dotnet.ps1 script was updated, now it is possible to:
       - Specify dotnet version patterns using regular expressions;
       - Specify any number of dotnet version patterns (previously it was 3 at most);
       - Optionally check if nuget.config file is generated;

The verify-dotnet.ps1 creates a temporary global.json file for each tested version of the .NET SDK.  It allows to build and run unit-tests in a sample c# project (e2e-test-csproj) using each installed version of the .NET.

2. The bash script verify-dotnet.sh was completely removed, as the only reason for it was to run in the Docker container here. 

3. The sample c# project sample-csproj was updated, now:
        - Project is targeted to the concrete .NET SDK using environment variable that is set in verify-dotnet.ps1`;
        - Unit-test is updated;

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.