Nullable reference types

[adambajguz]

Proposal: .NET libraries are moving towards using Nullable reference types. Are you planning to add them to InfluxDB client.

Current behavior: No nullable annotations in the libraries.

Desired behavior: Nullable annotations everywhere in the InfluxDB client.

Use case: Usage of nullable reference types in the library enables developers to write more stable (null-safe) code.

[powersj]

Usage of nullable reference types in the library enables developers to write more stable (null-safe) code.

Any idea how large of a change this would be? Would probably be happy to see a PR with the change.