.NET docs

[cretz]

What does this PR do?

Fill in scaffolding for .NET docs. Notes:

• Not looking for English editorial review in PR. Rather, we're hoping it can be copy/edited by a docs team member.
• Lots of the English parts and approaches to sections were taken from the existing approved documentation in order to be consistent and conform to known preferred/approved language/approach
  • Opened dozens of issues for docs team on issues found in other docs while writing these docs
  • Ideally any issues on docs/approaches that apply to more than just this PR should be solved generally instead of just here
• This mostly does not take a position on the reordering approach taken by the scaffolding (dozens of comments left on MVP .NET referential feature & inter-tech how-to documentation #2769, but that is unrelated to this work). For the most part, it just filled in blanks, but minor things were added/removed.
  • Note, the index was untouched, hoping docs team can decide what's wanted there, ref https://github.com/temporalio/documentation/pull/2769/files#r1586803748

[cretz]

We can remove this section pending that sample, or if it's urgent I can prioritize it