feat: Target .NET Framework 4.8 *v5*

[Dor-bl]

Change list

Target NET. Framework to 4.8 instead of 4.5 for both projects

Types of changes

What types of changes are you proposing/introducing to .NET client?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• New feature (non-breaking change which adds value to the project)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Documentation

• Have you proposed a file change/ PR with appium to update documentation?

This can be done by navigating to the documentation section on http://appium.io selecting the appropriate command/endpoint and clicking the 'Edit this doc' link to update the C# example

Integration tests

• Have you provided integration tests to pass against the beta version of appium? (for Bugfix or New feature)

Details

Since .NET 4.8 is the recommended Framework by Microsoft we should progress from 4.5.
In addition, seems like Azure Pipeline-hosted VMS doesn't support .net4.5 any longer.

[laolubenson]

@Dor-bl Can you rebase or merge master to test CI?

[Dor-bl]

@Dor-bl Can you rebase or merge master to test CI?

@akinsolb Build passed for master
https://github.com/appium/appium-dotnet-driver/pull/513/checks?check_run_id=8129258450