Dropping Dependence on `Newtonsoft.Json`

Using this How to migrate from Newtonsoft.Json to System.Text.Json

If .NET core 3.1 should be the minimum supported framework version supported; It would be a great time to drop Newtonsoft.Json and use System.Text.Json

In the code, there is only a few things to consider;

• Only used HttpEngine<T, TR> and in the two tests projects
• Remove the [JsonProperty] everywhere camelcase is by convention
• Remove the [JsonProperty] and replace with [System.Text.Json.JsonPropertyName] where properties are not conventional, like when using dashes.
• StringBooleanConverter Migrate to System.Text.Json
• DateRestrictJsonConverter Migrate to System.Text.Json
• SortExpressionJsonConverter Migrate to System.Text.Json
• StringEnumOrDefaultConverter Migrate to System.Text.Json
• StringEnumListConverterTest remove, convert to DayOfWeek ?

[vivet]

I have merged the PR, and working on cosmetics refactoring and ensuring everything works. I expect release within 1-2 days

[vivet]

Not really. I have been busy with other projects. Though, it’s good that you ask, cause i should really get this done 😄. I will see to it during next week