Move project to .net 8, remove Moq, update Flurl to v4

Move project to .net 6

fix: quick fix for netatmo api changesExtend CredentialManager to accept refresh_token and add warning messagefor deprecated GenerateTokenExample usage:```csharpvar clientId = "myClientId";var clientSecret = "myClientSecret";var accessToken = "myAccessToken";var refreshToken = "myRefreshToken";var client = new Client(    SystemClock.Instance, "https://api.netatmo.com/",    clientId,    clientSecret);client.ProvideOAuth2Token(accessToken, refreshToken);await client.RefreshToken();var stationsData = await client.Weather.GetStationsData();```Refs:#167#168

Update Netatmo.csproj

fix: fix licences mismatch with PackageLicenseFile

feat: .Net 5.0 🚀Refs:#113

fix setthermmode url

extened Indoor dashboard with humidity and upgrade sdk to .Net core 3.1

Add existing oauth2Token support (#32)Some services (as Alexa skills) manage the authentication and just provide the app oauth2 token.I added the oauth2 existing token support in "generate token" process.

Add AirClient to IClient