Convert from HAR file

[WeihanLi]

Is your feature request related to a problem? Please describe.

Similar to #51 , sometimes we may wanna generate request from a har file

Describe alternatives you've considered

dotnet-httpie convert <xxx.har>

• http://www.softwareishard.com/blog/har-12-spec/
• https://docs.fileformat.com/web/har/
• https://github.com/ahmadnassri/har-spec/blob/master/versions/1.2.md
• https://github.com/ahmadnassri/har-spec/blob/master/versions/1.3.md

[WeihanLi]

what if there are multiple requests, should we execute them all in sequence?
think it's a yes, and maybe we could support specify the sequence numbers