[DO NOT MERGE] .NET SDK custom log filter & platform compatibility docs

[adams85]

Description

Documentation for two upcoming developments in the .NET SDK:

• https://github.com/configcat/.net-sdk/pull/95
• https://github.com/configcat/.net-sdk/pull/94

Trello card

• https://trello.com/c/IxCFbq2j
• https://trello.com/c/L6VitCBe

Notes for QA

The .NET SDK reference has been changed, including some new links.

Requirement checklist

• [x] I have validated my changes on a test/local environment.
• [ ] I have added my changes to the V1 and V2 documentations.
• [ ] I have checked the SNYK/Dependabot reports and applied the suggested changes.
• [ ] (Optional) I have updated outdated packages.