Modernized and updated Dapr Workflows .NET quickstart

[WhitWaldo]

Description

Updated to both use Dapr 1.15.0-rc01 package, make changes specific to the latest bits, and otherwise updated the code to reflect modern .NET best practices (e.g. use of DI with primary constructors, internal sealed classes and source generated logging).

Issue reference

N/A - part of 1.15 endgame

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• The quickstart code compiles correctly
• You've tested new builds of the quickstart if you changed quickstart code
• You've updated the quickstart's README if necessary
• If you have changed the steps for a quickstart be sure that you have updated the automated validation accordingly. All of our quickstarts have annotations that allow them to be executed automatically as code. For more information see mechanical-markdown. For user guide with examples see Examples.

[alicejgibbons]

Once this is in, can we try with RC 5, since it has the necessary quickstarts changes?

[paulyuk]

LGTM. I love the modernization and minimalish code. thanks!